My observation is that no one with a single account will default such a small amount which is evidence of the defaulter. But it is not an easy way to find out who has an alt account and who has not. On the forum, we can't nothing judge which can save us. I have seen two users defaulted on the loan of Direwolf who has good rank as well as merit ranking but defaulted. So, we have nothing except to accept this type of loss until there are alternative accounts that are decreasing by being banned and defaulting on loan.
It is not your fault! Who could ever realize that a member would default a $100 loan. Next time do check their activities for a at least a year before agreeing to any loan request. If they are active every day then the chances of them defaulting would be less. This is not a fixed solution but it will give you reassurance. I hope this low life comes back and repays the amount he owns you.