Most things that are there is not as legit as what we think, it's been circulated with scammers and people that will steal information about you once you try to sign up with their site.
I would not be afraid the scammers. Logic sense can make out who is a scammer and who is not. What you need to be 'afraid' for is the police.
They are also present on those forums, looking for guys like you.
Buying bitcoin accounts in deep web is not a good thing. It is because in the deep web, all the illegal transactions are there. They are using proxy to hide their IP addresses from the hackers. What if you buy that account then you invested a somewhat high amount of BTC. Then the seller scams you and then he stole the account. Do you think you can tract them ? or even make them pay for what they did ? Of course not, what I am saying is that, you are not secure when using tor browser in any transactions. And compared to th normal web browsing. There are lots of dishonest sellers or buyers so I'd recommend not to get in touch with the Tor browser if you want to hold bitcoins.