I think my worst was $200, local “kid” who I’d met before 2-3 times....I’d always left the donation on a table top in plain view. On his last visit I went to the restroom, came back out and he and $200 were gone!
$20 or so a couple times when I prepaid “gas money” etc. EVERY time I did that I knew it was a mistake ahead of time but felt I was getting $20 of entertainment listening to the fiction leading up to sending the money and getting blocked/ignored.
Lessons learned, experience gained even after doing this for 30+ years!