Lenders offer a service which ppl need so it's got to affect when they've realised they've been scammed. Aren't loans without collateral ones you've lost most money in? If defaulters leave collateral you'll sell it to recover some funds because you've protected yourself from a full loss. If you don't take collateral you're risking losses from users you trusted because of previous loans they've repaid.
The chance of scamming is high by those who repay loan and trying to take large and after paying that asking larger and this way continue and once a time the user default the loan. Though there is an exception and but the chance of scamming is too high.