I have this situation with robosats and I honestly believe the best 1 line of defense method is NIP-05.
I believe some clients take it as a joke but its extremely useful to rapidly identify and discard impersonators.
And obviously the best but most expensive one is to use your WoT. Primal does a good job there by showing notorious people following an account, that's something reproducible with a 2nd level WoT of any user.