That's not what the "threat" said. It said that they would give them a list of people, it isn't obvious that hiring some random would have made them happy. It's not even obvious whether this wasn't just a convenient way to make some money for a friend.

I understand if you don't like how the person phrased it, but the goal of the DM was obviously to get the store owner to replace the AI poster. Assuming that they would have gone on a crusade because they didn't pick a "preferred artist" is pure unsupported speculation on your part.