I mean you joke but even if you're doing the best you can to return the money, you're right. You put it in escrow. If you've ever bought a house you've dealt with this but you can use it for a lot of things. I'm going to say as long as it's legal, ദ്ദി(˵ •̀ ᴗ - ˵ ) ✧

but thought experiment: like if there's no identifying information in there, if you were to go to the ~~bank~~ [credit union, sorry, not enough sleep or caffeine] and say hey, i found a wallet with no ID, it had a some obscene amount of cash, what would you need to tell them to quickly assure them you're looking for the owner. You'd go in and tell them you wanted to open a savings account in escrow of finding the wallet's owner with as minimal fees as you can. First, because you're returning a wallet and they think you're cute (you know they do you're returning a wallet), they'll help you with the minimal fees. Second, you're telling them it's a deposit in escrow while you're looking for the right person to give it to, so they should basically expect the account to open and close and accrue interest and that's it. Especially since it's someone's petit cash. If it does anything else they know to call you to let you know there's fraudulent activity with the account.

Then you've protected yourself while you begin your search for the wallet's owner, and after [your, not the wallet's. very important distinction right now] legal expenses to determine the appropriate waiting time before claiming the wallet. the search expenses, if any, they belong to the wallet. And shouldn't get attacked by any gangs of roving tellers.