The other issue is a legal one, what happens if you order a less than trafficking quantity of drugs?? Is it worth the police's time to track and prosecute you.
Finally, those who order on-line, most likely will not be using their real-name, and will not ship to their real-address (maybe ship to a letter-box of a vacant unit?) Even if the police tracked the letter, it is going to be very difficult to prove guilt, if they don't also camp outside the said letter-box.
In many ways I think that the enforcement of the prohibition drugs it up a creak without a paddle. The obvious solution, (legalize drugs), is in-fact the most rational also."