@AfricaHunting.com Jerome, this is a good bit of feedback. About every site on the Internet is dealing with the existential crisis of leaked credentials. I can guarantee that some of the fraud is from hacked accounts. All a perp has to do is find an email and password match on the dark web and then try them out on various forums. (people reuse their passwords on many sites)
The cure to this problem of hacked accounts is MFA / 2FA. (Multifactor authentication) This is where in order to log in you must receive an email, text message, or put a code in on an app on your phone. It ensures that a log in requires three things: something you have (A user name), something you know (a password), and something random that cannot be stolen (a one time pin code).
You could certainly pass on the costs of such technology to your user community. To buy or sell on this forum, you need a "premium" account that has this safety feature. That costs $10 a year to cover MFA security.
A cheaper alternative to the above is credential passing using a trusted password. (typically Facebook, Apple, and Google) You log in with those credentials and when you change those credentials, it changes your info here. The assumption is that if you're hacked, you forget about your 200 Internet passwords and focus only on the "main one" being FB/Apple/Google. Those three in turn allow MFA so they provide further security.
