I sold a near perfect used Lincoln only to get an angry call from the buyer a day later claiming I sold him a lemon. After he calmed down he told me he had gone

I sold a near perfect used Lincoln only to get an angry call from the buyer a day later claiming I sold him a lemon. After he calmed down he told me he had gone to the dealership to have the spark plugs changed. The dealership caused this problem. Given how easy it is to properly gap a spark plug, I can't help but think this is a scam when it is overlooked. But the scam only works if you don't get the gap too far out of spec. The victim should come back a month later, not a day later.