What is more likely, that law enforcement will coerce all clearnet providers into supplying all customer information to them, or that law enforcement will set up shop on a massive international drug selling site and hope that vendors use their service? It doesn't matter if your bags have serial numbers on them or not, you give the vendor a shipping address that can be put under surveillance. LE would be very smart to start selling vending supplies on SR, it is a surefire way to identify vendors stupid enough to order vending supplies on SR.