ORIGINAL: Sport_Pilot
The courts have ruled time and time again that selling a product to an end user that is illegal for the end user to use, even when not written in criminal code, is illegal and the seller bears liability.
Now it's your turn to prove your seemingly false statement (I'll bet you don't). In many states (and provinces) it is legal to sell a radar detector, but illegal to use it. If caught using it (in those states / provinces), it is the USER who is breaking the law, and as such, it is the user who faces the fine.
The issue of selling Tx crystals is the same way. It is legal to sell them, but ILLEGAL for the end user to swap them (unless they are appropriately certified / certificated).