You should have the sheriff run the v.i.n. or serial numbers (if it has one) through NCIC. That way, even if were stolen from outside his jurisdiction, even another state (your sheriff probably just checked the local reports), it would show up. Anytime a vehicle or piece of property is reported stolen to a proper law enforcement agency, the identifying number should be entered in NCIC.
It's sort of the national database we use in law enforcement.
Most, if not all, states share their records with it.
If it's clear through that, then you're probably home free.
At least this way you don't end up putting money into it, then finding out it was stolen from somewhere.
It's probably not, but better safe than sorry.
good luck,
anthony