Many premium products (or crappy expensive products) are bought by morons with money, simply following the logic that “if it’s expensive, it must be good”. Or because buying an expensive product, especially if you can show it off even once, signals “exclusivity”.
I’ve literally heard the phrase in a shop “I’d buy it if it was more expensive” for a perfectly fine product.
I recommend to sell the exact same product for 3 times the money, by adding an “X” to its name in the end, that should work.
Ask him why he talks shit about you, then fire him.