haggling. He said basically "I want it at this price X". Salesmen came back and said the best we can do is Y. He then said, well what if I told you I'm a costco member and want that deal.

Salesmen said that is completely different thing altogether (and should have mentioned that from the outset) and that he'd have to go get the manager. Manager comes out and they sell it to him at the costco price which was below the original X he said he wanted it at.

So yeah, I'd use it.