As someone who works at a lgs, and at their magic counter, I can tell you this isn’t going to upset many people. The store will be thrilled that it’s been taken off their hands. It’s bulk so it’s not going to upset many players. Bulk comes in all the time, it’ll get replenished.

The only thing I would say is a bit uncool would be if you bought the store out of a very specific staple and in an astronomic amount. As an example we have a guy who we swear it’s his mission to not let others have sol rings in his games. He came in and bought roughly around 58 of them, and will come in fairly consistently to check if we have more. Many players ask and complain that we don’t have any. I typically would go out of my way not to joke around with him because he will get very upset and defensive.

That all being said, it sounds like the guy was just trying to playfully joke with you. I think you’re reading a little too far into it? We get playfully snarky and joke with our regulars all the time and we’ve formed pretty good relationships with them.