Honestly, all my the loans that I have helped fund on Bjam are going well, I haven't even gotten 1 late payment or default yet.
I have fairly strict criteria to fund a loan and I dig around, but if i'm at all doubtful, I don't fund something even if its A graded
Remember that some people are shameless and just want to steal money... Some people are honest but rubbish at investing the money they have borrowed, so they're not scammers, but they wouldn't get a loan from a bank either.
Give it time. many pay for a while, then just disappear. In fact, you can now buy btcjam aged/verified/used with good rep accounts to scam with over in the digital goods section here now, so i'd say you've just been lucky so far myself.