If they were known scammers I am sure they will be banned already. If you think someone is a scammer just be extra cautious and make sure there is no way they can scam you
Exactly what N0ddie said, we like to think we do everything we can to make it safe.
TBH though if anyone is buying over a distance you have to use your head, if it is too good to be true - it probably is etc etc... I always prefer cash on collection, but people are different.