This paper explains why platforms such as Amazon and Visa rely predominantly on ad-valorem fees, fees which increase proportionally with transaction prices. It also provides a new explanation for why ad-valorem sales taxes are more desirable than specific taxes. The theory rests on the ability...

This paper investigates a puzzle and possible policy concern: Why do platforms such as eBay and Visa that enable the trade of goods of different unobserved costs and valuations rely predominantly on linear ad-valorem fees, that is, fees that increase in proportion to the sale price of the trades...