Introduction
With the acceleration of digitalization, e-commerce platforms have become the main channels of trade for both consumers and sellers. These developments have led to the diversification of services offered in marketplaces and the optimization of transaction processes through complex algorithms. In this context, BuyBox practices, which directly influence consumer choice and shape the visibility competition among sellers, constitute one of the applications that must be carefully assessed from a competition law perspective. Especially in multi-seller platforms such as Amazon, Trendyol and Hepsiburada, how BuyBox algorithms are designed, and whether these algorithms lead to risks such as discrimination among sellers, self-preferencing, or price coordination, remain under the scrutiny of competition authorities. This article examines the effects of BuyBox practices on competition law in light of recent decisions rendered by the Turkish Competition Authority concerning Trendyol and Hepsiburada, as well as precedent-setting assessments of foreign authorities.
- The Concept and Functioning of BuyBox
The BuyBox algorithm highlights the offer of the seller who would provide the highest benefit to the end consumer in cases where multiple sellers offer the same product. The ranking provided by the algorithm creates a visibility advantage and directly impacts the commercial success of the relevant seller.
In Türkiye, multi-category online marketplaces such as Trendyol, Hepsiburada, Amazon, and n11 actively apply the BuyBox algorithm. For instance, Amazon uses the BuyBox area as the section on the product detail page where consumers conduct transactions via the "Add to Cart" or "Buy Now" buttons. Transactions carried out through this area are directed to the product of the seller who wins the BuyBox, thereby granting the relevant seller a significant competitive advantage. 1
The criteria for determining which seller the algorithm highlights vary from platform to platform. In general, these criteria include product price, seller performance score, the offer of free shipping, and delivery time.2 Among these, product price appears to be the most heavily weighted criterion.
In an effort to win the BuyBox, sellers lower their prices, aim to deliver products faster, offer free shipping options, and try to improve service scores related to customer satisfaction. As a result of these dynamics, the prices consumers pay for products decrease, service quality improves, and consumers' search costs are reduced. Ultimately, the BuyBox practice contributes to competitive market outcomes in these respects.
- BuyBox Practices in Turkish Competition Authority Decisions
Under this heading, recent decisions by the Turkish Competition Authority ("TCA") concerning Hepsiburada and Trendyol will be addressed.
In the investigation conducted by the TCA into Hepsiburada's BuyBox practices, the investigation was concluded by accepting the commitments offered by the undertaking to eliminate competitive concerns. The decision assessed that Hepsiburada's BuyBox mechanism affects seller preference by ranking different sellers offering the same product based on an algorithm and that this system may lead to outcomes similar to price fixing and hub-and-spoke cartels. The TCA noted that the automatic pricing tool, particularly through the "Match BuyBox Price" option, could produce anti-competitive effects. Accordingly, Hepsiburada committed to eliminating this option, not requiring the use of automatic pricing, excluding it from the BuyBox algorithm, and refraining from sharing seller data. Upon finding the commitments sufficient, the investigation into Hepsiburada was terminated.3
Similarly, in the investigation conducted by the TCA into Trendyol's BuyBox practices, the TCA accepted the commitments proposed by the undertaking and concluded the investigation. The decision indicated that the BuyBox mechanism ranks multiple sellers of the same product via an algorithm and that this system, through the "Match BuyBox Price" option, could result in price fixing and lead to competition violations. The TCA evaluated that this structure could influence the decision-making processes of sellers in a manner similar to hub-and-spoke cartels. Within this framework, Trendyol committed to not making the automatic pricing mechanism mandatory for sellers, eliminating the "Match BuyBox Price" rule, excluding this mechanism from the algorithm, and ensuring the confidentiality of seller data. Moreover, Trendyol will carry out information and training programs for sellers, provide competition law training to its employees, and submit independent auditor reports to the Turkish Competition Authority for a period of three years. The TCA found these commitments sufficient and concluded the investigation.4
- BuyBox Practices in Foreign Authority Decisions
In this context, the approaches of foreign competition authorities to BuyBox practices will be examined, and the differences between these two approaches will be analysed.
In a lawsuit filed in 2023 by the U.S. Federal Trade Commission and 19 states against Amazon in the Western District Court of Washington, it was alleged that the company had unlawfully monopolized the online store market and online seller services market through pricing algorithms, thereby harming consumers. The lawsuit claimed that Amazon restricted BuyBox visibility from third-party sellers offering lower prices, placing those sellers at a serious competitive disadvantage; copied prices of rival retailers to distort competition in the market; and triggered rival price increases through an algorithm called "Project Nessie," thereby raising consumer prices. The Court concluded that these allegations plausibly demonstrated a restriction of competition, rejected Amazon's federal-level objections, and decided to proceed with the case.5
In investigations conducted by the European Commission into Amazon's BuyBox and Prime practices, the Commission concluded that Amazon held a dominant position in online marketplaces in Germany and France and abused this position. The Commission found that Amazon systematically favoured its own retail products and sellers that opted for Amazon's logistics services through the BuyBox practice, thereby reducing the competitiveness of independent sellers. It was also noted that Amazon's use of competitor seller data obtained in its capacity as a platform operator posed a serious risk of competition law infringement. Accordingly, Amazon committed to making a second BuyBox offer visible, ensuring neutrality within the Prime program, protecting data of independent carriers, and facilitating sellers' exit from the Prime system. The Commission made these commitments binding on 20 December 2022 and decided that they would be implemented across the European Economic Area for a period of seven years.6
- Potential Competitive Concerns
Although efficiency gains can be achieved through BuyBox practices, several competitive concerns may arise. Under this heading, tacit collusion among undertakings will be addressed first. In this framework, the designation of the BuyBox winner not through price competition but through a direct or indirect agreement among rival sellers, or through unilateral interventions by the provider, raises serious concerns under competition law. Especially when sellers, without establishing direct communication among themselves, shape the BuyBox practice under the provider's guidance, this enables undertakings to coordinate their present and future behavior. Such a collusion is considered to constitute a restrictive agreement, concerted practice, or decision under Article 4 of the Act No. 4054 on the Protection of Competition ("Act No. 4054") and is therefore deemed unlawful.7
Additionally, if undertakings utilize the same dynamic pricing system, there arises a significant possibility of forming a hub-and-spoke cartel through such systems. In this regard, the provider's offering of a single algorithm and encouraging its adoption by competitors in the market leads to convergence in the pricing of the relevant undertakings.
In such a system, although there is no direct information exchange between competitors, the centralization of price determination within a single algorithm allows for tacit coordination. This structure, where the likelihood of deviation from collusion is reduced, creates an environment in which competitors can instantly monitor price changes, and if one undertaking lowers its prices, others can take countermeasures shortly thereafter. In this context, price monitoring software and dynamic pricing systems increase the functionality of hub-and-spoke cartels, rendering horizontal coordination practices. Accordingly, the effects of such algorithms on competition must be examined carefully, and the role of providers should be evaluated as a critical factor in establishing concerted practices among undertakings.8
Finally, within the scope of algorithmic harm theories, it is acknowledged that the adverse effects of algorithms on competition may materialize not only through coordinated behaviour but also through unilateral conduct. It is observed that foreign competition authorities have subjected algorithms to intensive scrutiny, especially within the framework of abuse of dominant position. This raises serious concerns that digital platforms establish economic power through algorithms.
In this regard, algorithmic exclusionary practices may involve predatory pricing strategies aimed at excluding competitors from the market, prioritization of the undertaking's own products and services, implementation of discriminatory discount policies, and market foreclosure effects through tying or bundling practices. On the other hand, algorithmic exploitative practices may take the form of excessive pricing, imposition of unfair commercial conditions, and price discrimination. All these are considered to constitute an abuse of dominant position under Article 6 of the Act No. 4054.
Conclusion
Although BuyBox practices yield improvements in consumer welfare, these practices appear to give rise to various exclusionary and exploitative effects related to tacit collusion, hub-and-spoke cartels, and abuse of dominance. Indeed, the decisions of both the TCA and other authorities have highlighted such effects.
In response to these risks in digital marketplaces, it is observed that competition authorities have employed different competition law instruments. In the U.S., a more traditional competition law approach has been taken, focusing on infringement findings and the establishment of legal liability through judicial proceedings. In contrast, the European Commission and the Turkish Competition Authority have aimed to directly influence the competitive balance through the commitment procedure and the imposition of behavioural obligations. Furthermore, while the FTC case provided a more detailed examination of the structural effects of algorithmic pricing on competition, the Commission decision emphasized competition concerns arising from discrimination and data use.
Going forward, competition authorities are expected to intervene more closely in algorithmic decision systems and to increase transparency obligations for platforms. Therefore, practices such as BuyBox will continue to occupy a central position in competition law as strategic mechanisms that shape not only intra-platform competition but also the overall market structure.
Footnotes
1 https://satis.amazon.com.tr/satici-blogu/buybox-nedir Access Date: 25.04.2025
2 https://akademi.trendyol.com/satici-bilgi-merkezi/detay/buyboxi-etkileyen-metrikler Access Date: 25.04.2025
3 TCA's Hepsiburada Decision, 03.10.2024, 24-40/951-410.
4 TCA's Trendyol Decision, 03.10.2024,24-40/950-409.
5 U.S. Federal Trade Commission and 19 States v. Amazon.com Inc., Decision: 2:23-cv-01495, U.S. District Court for the Western District of Washington, Dated: 30.09.2024.
6 European Commission, "Antitrust: Commission accepts commitments by Amazon barring use of marketplace seller data and ensuring equal treatment of sellers when ranking offers for the Buy Box and Prime eligibility", Case AT.40462 ve AT.40703, Dated: 20 December 2022.
7 TCA's Farmakozmetika Decision, 05.07.2023,23-29/563-190.
8 Rekabet Kurumu Uzmanlık Tezleri Serisi, Geleneksel ve Dijital Pazarlarda Topla ve Dağıt Karteli, Tülay Şimşek Sarı, October 2022, Turkish Competition Authority – Ankara.
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