Most of the time, people who are selling accounts in this forum, are just re-selling accounts they've purchased. So it's typically harder to get an account back unless your the original owner. It can still be banned easily though.
There's always a risk, I recommend buying from people who have good TBM ratings, but like the post above mentions, there are some tricky people out there.
1) Buy from trusted sellers (high TBM's) -- Personally, I don't even trade with any1 who has a negative rating
2) Use middleman
3) Hope it works out
My recommendation is to buy an account from friends in the server. For Instance, if you play on GA1 and you're looking to just get a better ship on GA1. Buy it from friends in a teamspeak, I've always had a good experience that way. It's not always possible though.
Safe trading!
Regards,
Snow