Oofta
Legend
It's a crime, but a less serious crime than if someone dies, and carries a lesser penalty.
In this case though, it's more akin to selling defective second hand cars. In which case if the car's breaks fail, you can argue caveat emptor applies.
The shapechanger will eventually get hungry enough to eat someone. It has to in order to survive, it's not going to starve itself to death. You're minimizing what they did significantly.
It's more like selling cars that you guarantee will eventually explode while running, likely killing everyone inside and quite possibly a few bystanders. As far as punishment goes, there is absolutely no reason to believe this group will stop selling these disguised books. If they are not stopped, more innocent people will die because more shapechanger books will be sold.
Proper punishment is a separate issue and is going to vary depending on how the DM runs the justice system. I have no idea where you got the text for how the judiciary works, but if it's not a 5E source it's no longer canon. That, and of course people are going to run it with different assumptions. But crime and punishment in a D&D campaign world is a whole other topic.