I once bought a used guitar from an old friend (he's another shady guy). After taking the guitar home I notice the serial number is scratched off. I think oh crap he sold me a hot guitar! So I call the police and speak with a detective and tell him how I bought this guitar with the serial scratched off. The detective asks me if I know its stolen or just suspect that's the case. I say I don't positively know but come on it must be stolen. The detective says well you don't know its stolen and there is no way to find out without the serial number. I say ok, well what should I do? He says I'd tune it up and play it!

If you don't know it stolen just assume it's not and enjoy it.