Yep, you're fine. Taillight warranty applies. If you buy a gallon of milk at the store, you can see it, check the expiration date on site, check for leaks, whatever. Once you leave the store with it, if you drop it on the ground and it breaks open, it ain't the store's fault. You buy yourself another gallon of milk if it's that important.
They came, saw, played, *inspected*, disassembled, loaded, paid for, and took the machine. Whatever happened after that has no impact or bearing upon you. To quote Statham: "The deal is the deal."
Do yourself a favor and don't deal with this idiot again under any circumstances. You don't want them coming back.