I agree, we need to get some countermeasures against them.
But then again this site is not a trading website, specialized on selling,buying trading.

I can see another way of dealing with this: Removing the marketplace section.
This website's main goal is to give support and knowledge about the hacks TMC offers, not to sell your stuff.

As we moderators confirming sellers is like... no use. He can play the nice guy, kind, fast trader and when he gets our "seal of approval" he goes and scams everyone and who will be blamed? Us, or the person who gave him approval.

About showing sensitive information such as IP,Subscription type etc.... i'm not sure but its kinda against some laws or ToS. I mean these are personal info, which shouldn't be shared to third party/person, or announce it make it public.
Even i can't see people's IP so i can't even filter people with same IP, who might just re-buy the cheapest cheat and do it all over again.

What i can recommend is:
-If the guy doesn't have much vouches, don't even trade with him or be really careful.
-Obvious bumps and "Thank you good and fast trade" messages are fake, or its from a friend of him.
-Be really careful when sending money as "family and friends" option on paypal, its really annoying when you have to waste time to talk with paypal about your issue.
-When you see someone who has the same username on skype and the forums.... 99% scammer. Why? Because when you buy hacks you WONT use your real gamer name, what your friends. Specially if you play any multiplayer game on clan level. Nobody wanna show up on TMC by simply googling his nickname.