Placing an offer to sell my BTC and get XMR, it prefill 15% security deposit for both traders and this % is customizable. Why not to set it to 0% if both payment methods (BTC, XMR) are irreversible and why Haveno-reto does not set it like that automatically?
Existing offers of this currency pair usually has 15% or 40% deposit and the fee 1.8-20% which is also weird, I would expect people would be willing to trade like 0-1% just to cover the crypto. fees.
The deposit protects against rogue arbitrators. At 10 arbitrators and 15% deposit, it is mathematically not profitable for any one of them to attempt scamming people.
Prices are higher because who would accept potentially dirty coins in exchange for clean Monero? For fiat currencies there is either some amount of chargeback risk or you have to deal with mailing physical cash, nobody would do that for a $2 gain.