Bitcoin Forum

Can someone explain to me the value of buying a Hero or Full member account?  Why so many forsale?  Is it even legal? 

scamming and spamming........

yes it is legal and most of the accounts being sold is used for joining signature campaign that will give them some extra money while posting in this forum (but some users buy an account just to use it for scamming)

It is legal sice it is not against any bitcointalk tules but not everyone encourage buying and selling of accounts because some people use it to scam while mostly bought accounts are used in spams.
The value of an account differs depending on it's status an reputation. You can try and check an estimate at bitcointalkaccountpricer.info.

It's clearly not nice. And if found, such accounts are usually marked with negative trust. But it's not actually illegal.
The use? From scams (lending collateral, ICO or other business proposals) to signature campaigns (where the payout grows with the rank).
For signature campaigns people usually buy accounts with potential high level, to save time.
For scams the actual high levels make more sense, I think.

As i do know people do sell the accounts in the general to join a signature where they expect to be able to roi, but some high ranks accounts are purchased just to ask for a loan and scam others, its allowed, but if the account get exposed it gets the feedback almost instant.