My old 5s is dying and I'd like to buy a used iPhone 8+. Have any of you bought a used phone off Facebook, LetGo, etc.? I know to check for water damage, get the IMEI, and make sure it's compatible with my carrier (verizon). Is there anything else I should do?

I've never bought something so expensive secondhand before, so it makes me nervous. But I can't really afford to buy new, so fingers crossed I don't get burned!