This is worrying because it means consumers have no protection. I think in most transactions the seller is well-known and has to worry about reputation effects

This is worrying because it means consumers have no protection. I think in most transactions the seller is well-known and has to worry about reputation effects, while the consumer may as well be anonymous. In which case consumer protection is not that important. For cases where both parties are anonymous/untrustworthy, you can use a protection scheme like escrow. That doesn't work when the payer can take his money back after the transaction, of course.