Btcjam is a cesspool for scammers and I would advise anyone considering to invest in their loans not to. I am not really sure about the other Bitcoin related websites however I would think it would be the case generally speaking.

One major problem with Btcjam is that they force you to collect on defaulted loans. If someone borrows $5,000 from 100 people, borrowing $50 from each person, then each person would need to invest additional money to only potentially recover a small amount, likely needing to invest the entire amount they are attempting to collect. A better solution would be for BTCjam to collect on behalf of the borrowers as a whole (or employ a collection agency) which would allow them to realize economies of scale when collecting on delinquent debts and it would obviously be much more worthwhile to collect on a $5,000 loan.