how to prevent fraud?
bisq has witnesses to confirm p2p trading.
A block explorer would show you the addresses blocks mined, time existing, transaction list and #FB feedback for his transactions. Also people can compile a 'trusted' list of addresses they have done buisness with. Plenty of ways.
it seems that after the thing.
most DEX services have temporary deposit system to prevent fraud before the thing.
cryptocurrency service must not be based on inherent goodness but inherent evil.