I don't know about nowadays, but when I sold auto parts, NOBODY would take back an electrical part, especially if there was evidence that it had been installed.
Would YOU want a "new part" that had been tried about by someone? EIGHT someones?
This is NOT how you troubleshoot a problem. I've even had a customer bring back a greasy, scratched up gas filled fuel pump. I said "what's the matter with it?" He said, "nothing, it wasn't the problem."