Did you pay the same amount as if you bought it from PSM. I'm assuming not, otherwise you would have just bought it from PSM.

So a seller, sells you a chassis that is NEW for less than NEW and there's one hole not counter sunk from the factory (not that the seller did anything). I personally would just countersink the hole and move on.

You can get mad at the seller all you want but he sold you a new chassis. If it was new, then he probably didn't mount it up so he would've never caught the issue.