Clone Hostility
To them it is cheating. You can get the experience without the expense. It is why the first question out of most everyone's mouth when you see open the hood on an a-body and it has a 340 is "is it numbers matching?" I used to think that way too until I grew up and realized that only matters when you sell it. So if you aren't buying it why not ask what his quarter time is how it drives or any interesting stories about the resto. Isn't that a little more interesting than whether it was the original engine?