I found the following approach very interesting: * Generate a random price in the acceptable range (but don't tell the user about it) * Let the user know that

I found the following approach very interesting: * Generate a random price in the acceptable range (but don't tell the user about it) * Let the user know that you made up a price and let him enter what he would pay * If the user entered a higher price than the random one he gets the product, otherwise he doesn't Of course this only works if you keep the user from trying to do this multiple times, for example by offering an invite-only system and giving every invitee only one chance.