Commission Structures, Fee Policy Changes, and Their Effects on Seller Entry, Pricing Strategies, and Retention in Platform-Based Retail

Abstract

Platform-based retail increasingly relies on fee schedules that combine ad valorem commissions, per-transaction charges, subscription fees, and optional paid services such as advertising and fulfillment. These instruments are frequently revised as platforms search for revenue stability, category expansion, and perceived fairness across heterogeneous sellers. At the same time, sellers respond to fee policy changes by adjusting entry timing, pricing and promotion intensity, assortment breadth, and the choice to remain active or exit. This paper analyzes how commission structures and fee policy changes propagate through seller decision problems and market outcomes in platform-based retail. The approach integrates a structural model of seller entry, pricing under demand uncertainty, and dynamic retention with an empirical design that leverages discrete fee revisions and heterogeneous exposure across categories and seller types. The model clarifies how shifting from ad valorem to fixed fees changes marginal incentives, pass-through, and the composition of entrants, while fee increases in optional services can alter measured commissions indirectly by affecting effective marginal costs. The empirical component outlines identification strategies for isolating causal effects in the presence of concurrent platform interventions, including shipping policy updates, ranking algorithm adjustments, and seasonality. Counterfactual simulations quantify trade-offs between revenue, price levels, variety, and seller churn under alternative fee menus, emphasizing conditions under which platforms can reduce distortions without triggering large exit waves. The analysis highlights mechanisms linking fee design to long-run marketplace health through selection, learning, and the endogenous survival of sellers.