Someone else needs to walk in there and argue with this guy. The more people who do it, the more he'll "Get it" that people are seeing right through him.
Agreed- or e mail them. He does have to be careful , he could be breaking the law- if he is offering "Discount", " Sale" or "Reduced" items there are strict laws that need to be followed.
I went into a garden centre today that sells fireworks (full price) and asked of they would consider doing me a discount. She said no, because they sell £100s worth to some people, and they usually sell out. Which is fair enough. A straight, honest, business based answer.