In the last years, the authority that regulates economic competition in Mexico has investigated the share of digital platforms in local markets. These investigations have a particular focus on the classic rationality of Law & Economics. However, utilizing a behavioral economic approach allows us to detect cognitive biases that have been unknown from a traditional perspective, but that affect the efficiency of markets. This aspect has not been enough explored in the Latin American region. Pizza restaurants establish a contract with UberEats whereby pizzas are sold. This article analyzes a random sample of these contracts offers in UberEarts to estimate Herfindahl-Hirschman Index. Through a statistical test, this article found an atypical concentration of pizza restaurant offers in the first positions. This concentration abruptly changes in the next positions. This article utilize behavioral economic models to analyze this irregularity and found an explanation related to cognitive bias.