If you are considering to accept forum accounts as collateral for loans, then I would suggest that you don't. In my experience, the overwhelming majority of loans where an account is used as collateral will default, and the loans that do not end in default will very often result in the borrower subsequently asking for a larger loan then what their account is worth (e.g. the 1st loan was a confidence loan).

If you can get a signed message from an old address associated with the account being accepted as collateral, then the risk of someone coming back to claim the account was hacked is low, especially if the account has been posting somewhat frequently recently. Although you do have the risk that the account is involved in some kind of scam that will result in it receiving a negative trust rating.

If you are interested, or would consider buying forum accounts, either to farm or to resell then you would probably be better off opening a [WTB] thread in digital goods. You will probably be able to buy the accounts for as much, or less then you would be able to if you were buying them via loans, and you would not be forced to have the accounts sitting idol while you are waiting for the loan to default. Additionally, a WTB thread would allow you to keep the prices you are willing to pay more private, witch will aid in your ability to negotiate with sellers.

If you are truly interested in lending BTC to users, then you would really almost only want to consider accepting stable, established alt coins, or lending to people who have significant amounts of reputation.