Of course you can just register yourself for free, to become a higher forum rank you can donate if i remember first you need l33t (10$) then you need to have a certain number of forum posts and some rep to buy the next rank (uber),
what is the advantage of higher rank in such forum?
1. More trusted
2. More features: Give rep, Trust scan, no post restrictions
3. Badge under your username
4. Colored username
5. More swag
Anyways, there is a huge risk involved in trading HF accounts. It's clearly stated in their rules that selling/trading accounts is strictly prohibited. Like said, these accounts get banned immediately and need the original owner to verify that they still own the account. If that's not done, the account will get banned permanently.