When it comes to wallets and those having some value in it, it’s with extreme caution but yeah, there are those that are in this situation for real and also, there are those that would want to take advantage of this to hack the wallet of other genuine users out there.
That’s what makes this some worth challenging and probably the reason why you got your account banned on Reddit.
Is there any way I could gain trust around this? I wouldn't be able to run it for free forever as GPU time isn't cheap, but I thought asking for whatever donation the user wanted after a successful recovery could offset the costs.
Since you posted here the only way users will trust you is to gain reputation here. You dont just run a business ( micro sideline) involving funds without trust rating here.
Gaining trust here is the first step towards any form of positive development that might emanate from OP as, everyone is obviously under a watchful eye for some maliciousness until proven otherwise.