Loaning people your money is a good way to lose it all quickly and all for what? A tiny piece of interest? Most people will likely just take out loans to pay them back until they build up enough confidence to take a big chunk and run off with it.
not if you have a policy of "never lending someone big amount of bitcoin without a valid collateral". you can sell the collateral if they default, and limiting the loan with no collateral to 20% of their account's worth will reduce your risk.
The best way is never trust anyone if you really willing to lend your money. Sometime there is someone that want to borrow your money in little amount, and in promised time he pay you with the interest. He borrow your money repeatedly and pay back on time. Then someday he borrow high amount money from you without collateral because you believe he will pay back on time like usual. But, he never come back and run with your money. This situation often happens.