There may be other circumstances in which the serial number might be checked
I'm curious ... what oher circumstances?
A couple more might be ...
an insurance claim comes to mind.
Even so, the odds of purchasing a stolen gun and then having any of the reasons stated for having a gun checked have to be pretty remote.
And having one checked in any of the circumstances above, losing a few hundred dollars on a purchase will be way down the list of things to worry about.
A couple of assumptions in my thoughts ... the buyer is a person of decent moral character and purchases from a reasonably reliable source.
If the buyer is a meth head and the seller is selling out of the window of a van as he drives by, then the odds go down significantly.