Imagine you're selling a tool that lets players win every game.
Then imagine someone else starts selling another tool. Anyone who buys that other tool is now able to beat the players you promised a win to, AND they're not giving you any money for it. This damages your reputation, which in an underground market is probably your most valuable resource. So not only are they not paying you, but they're robbing you of future sales by damaging your rep.
Wouldn't you put in something to prevent users of your newest cheat from being cheated themselves?
Then imagine someone else starts selling another tool. Anyone who buys that other tool is now able to beat the players you promised a win to, AND they're not giving you any money for it. This damages your reputation, which in an underground market is probably your most valuable resource. So not only are they not paying you, but they're robbing you of future sales by damaging your rep.
Wouldn't you put in something to prevent users of your newest cheat from being cheated themselves?