Firstly, this stuff isn't a scam. I've gotten 2 ipods through similar sites with no trouble at all.
Secondly, no one is forcing you to sign up. If you don't like using your credit card online, fine, this isn't for you. No big deal.
Thirdly, I don't know how you are getting PMs, but have you tried replying to them? Or alerting a Moderator about them? It's not the post that's doing it, it would have to be someone specific.
Good luck.