Yeah really, cgtrader should ban every seller that's daring to set their prices at will, because that's a crime in MANY countries (probably Iran and North Korea)... LOL.
If you already monitoring prices of products that you plan to purchace, then what is your problem? If you see that certain seller's discount is a fake one, then simply don't buy from him. At least you have a choise. In my country all the food items are selling at discounted prices all the time, yet food prices are biggest in the whole freaking EU. Every person is aware that most discounts are fake, yet many rigorously hunts for biggest discount, like it was Olympic games. It's a free economics you know, if you don't like it, you don't buy it.