I haven't looked too closely at how this works, but regarding your concern, don't other printing services run this risk too if that's illegal? like Kinkos, FedEx, library printers?
To be sure, it's a pretty loose contract and you could probably get away with printing a small amount of copyrighted material. But it at least shifts the liability onto the customer so the retailer can always point to the agreement and say "hey, they said they weren't printing anything illegally; that's on them for lying."