[quote name='cg1407']If you are buying a share from someone else they can never access your account correct? So the only way to get ripped of is if they take your money and dont give you access correct? Sorry for the noob question.[/QUOTE]
By access your account, you mean your personal, main PSN account? If so, no, they never have access to that and there's no possible way they could, as accounts on the same console don't associate with each other in any way. The only way to get ripped off is if they flat out take your money.
Although I have one account with a weird problem...I've downloaded everything that came with it, but when I try to redownload something, it says it has been activated too many times. I'm not sure if someone tried giving it to a 6th person or what, but I can't do anything with the account now. But the stuff I downloaded initially works fine.