Dice could easily be MIS-constructed in such a way so as to make one face or two opposing faces slightly heavier. In the manufacture of dice, the acetate removed during pip construction is supposedly replaced with an identical mass of paint. This "cheating" could be done on any face or faces of the dice. On tribal lands not overrun with bureaucrats, they could probably get away with this sort of thing pretty easily, if they wanted to. More sevens would in general help the house. If too many started betting the Don'ts, these dice would disappear, unless they happen to be murdering the Don't players at come out. As 7uwin had already stated, there's too much at risk if a corporation gets caught at this - hell craps isn't even the major game in town anymore.