A trade is basically a contract with a receipt as proof & we generally treat them as refundable in the short term based on the idea that the buyer's expectations must be met. I suspect we will eventually get some sort of 2 party escrow system for 2nd layer retail payments that will eliminate most fraud problems before the txns are even complete.

IMO the contracts today that no one reads are more a product of a fiat legal system where laws are designed to confuse & tax & complicate transactions rather than facilitate trade & clarify things.