There is nothing wrong with giving the stink eye, giving off a vibe, coughing the word "dick ehem" when he walks by. Also, when he asks about your machine for sale with the price tag on it that says $600, you look him straight in the eye and say $1000 bucks as you pull the price take off and put it in your pocket.
Make the hobby no fun for him. aint that hard...... Hell vendors can blacklist him too. I have a blacklist. Dishonest, or people I send a replacement and they don't return their items as agreed, people that are disrespectful, or are difficult to work with.
This guy is proven dishonest, no one can afford to deal with him. Blacklist the F'er
Hard to stay in the hobby if no one will buy from you or sell to you