I'm leaving BTCJam forever, putting my money here was one of the many mistakes I made with my bitcoins that ultimately made me end up with 1/5 of the bitcoins I once had.
Here is the final view of all my investments there at the moment that I'm withdrawing the rest of the bitcoin that are left in my wallet, I don't expect to recieve anything else from the people who defaulted anymore.

I'm not saying that everyone is going to lose money there, this is just my personal experience using this site.
I've personally only invested in a couple of loans, but even with my little experience it is pretty obvious to tell which loans are/aren't legit. If you only loan out your BTC to people with good scores and a solid loaning history, you are unlikely to get scammed. The accounts without a profile picture that offer insane interest rates are going to default every time, end of discussion. However, if you stick to the safe loans, you can easily profit.
What you say is total bullshit, i only invested in A and B loans and only when the people had really good feedbacks and even on that Loans you have a quite high Rate of People who do not pay back the Loans.