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 might be better for you to tighten the loan rules for new borrowers which aern't prominent users (if you agree to their proposal), eg limiting them to a smaller amount eg $50 or less for a few trial loans until you have cleared any doubt that the user won't try cheat.
It seems that the user's status as a promoter of a certain campaign is no longer a reliable guarantee to give them a loan especially if they have only been accepted for a few weeks, the fact is that we don't know whether the campaign salary is only their main or side income.