You can't set a proper price cap atm without the help of IMC to mechanically program it into the game. The admins though do have the power to confiscate items from your possession. The only way to reduce prices is to announce an official notice of a price cap and punishment for breeching it. Think of how laws are passed as a deterrence in society if there is no punishment will laws work definitely? No! If I say you can't smoke in this area but do not give a fine will people bother about it if it inconveniences them?