Any thing with a mouth and teeth can and will bite. Buying from a good rat breeder/pet store will prevent this from happening most of the time. If the rat isn't hungry, ti's not going to look for something to eat when placed in the snake's enclosure.

But once the snake strikes and coils all best are off. But lets face it, these snakes have been eating live food forever. They must know how to do it properly, since most never seem to get bitten.

I think most snakes are bitten because the rodent is left in the enclosure too long. So if your snake doesn't eat the rat in say 2 hours (this time frame is something you will have to determine), remove the rat and feed it to another snake. If none of the snakes eat it, you will have to dispose of the rat somehow.

Good Luck!
Jim Smith