OUCH! I have this nasty fetish of being able to fix what I buy. probably why I stick to military lineage weapons.
Having said that, there was this one SKS, red bakelite stock, blade bayonet, S/N 700,000,0001 that was just cursed. We literally broke a nearly new rifle down for parts!
If you picked it up with the safety on, the trigger group fell out, if you turned it on its right side and thumped it, the top cover retaining pin fell out, the firing pin liked to hand so on occasion it slam fired too, damn near blew my head off! the parts fit well with other SKS we had so obviously the receiver was way out of spec. I sold it as a barrel for fifty bucks an a gun show.