"If it goes back more than once and they can't fix it, demand a new gun."
yeah... good luck with that, re: Taurus CS
hint, Lifetime Warranty = right to return as many times as you want to, does not equal new gun to replace
PS
Old Fuff is right as usual.. be sure the gun is clean (under extractor, ejector rod not unscrewed, etc., the obvious stuff). But unless OP is a gunsmith, or even if he is (though he would not likely be asking this question), and if he sold a NIB gun to a customer, why on earth would OP NOT send it to CS (as in arranging for customer to send it to CS, user friendly shop owner) ?
If b/c gap is so tight, that just 25 rounds of rimfire thru a prior to shooting clean gun binds it up due to face fouling and/or 'heat', it is too tight.
if inclined to take a file to it, suggest you let the gun owner do that, it's owner's warranty, not seller's, absent seller's personal contractual promises to the contrary
or Taurus CS
not the seller, he don't own it... but he just might own it if he starts filing on it
"hope he doesn't come in wanting to trade it in on something."