Is there something (a filter or algorithm) filtering the fraudulent SEPAs, at the country/bank/IBAN. Including a payment option that opens the doors to the chargeback/dispute is a little risky for people.
I see Bisq has an arbitrator system but nowadays with a SEPA it usually take 24-48h
Almost 6000 SEPA Euro trades have happened on Bisq so far. Approximately 1% of those have gone to arbitration. 0 of them have been due to chargebacks.
It is true that in theory SEPA transfers are not final and can always be reversed.... but in practice bank policy in Europe is to allow cancellation within the first 24hrs and after that only ever reverse SEPA transfers in cases of fraud or crime. So it is very, very rare and if it happens more than once to the same account then bank will probably close the account...
Even so it is possible to block onion addresses on Bisq or "blacklist" payment accounts... but this block or any other reputation-based security feature is by nature incomplete as there is no permanent identity on Bisq.