yeah, i mean, a buyer in america or EU shouldn't have jack shit to worry about. tor is a legitimate service and perfectly legal
It is perfectly legal to drive a particular sort of car as well, but that doesn't mean LE wont check DMV records when they make one of their suspect set sizes, if a certain type of car is frequently spotted near a certain type of crime scene. The rarer your car is the more prone you will be to being identified in this way. The less people who use Tor near where you ship from, the more prone you will be to being identified in this way.
After you are identified in this way, you will likely be put under various degrees of surveillance until they build a case against you from it. They will probably also watch your mail extra closely. They may manuever agents in their human intelligence networks (snitches and undercovers) closer to you and try to get you to do little illegal things. Then they might get your connection tapped and do a website fingerprinting attack to find some % probability that you are a certain user on SR (sites loaded through Tor, even though they are encrypted, have been identified with 60% accuracy with traffic classifiers, chaos computer club made the best one so far). They could bug your computers or what the fuck ever.
The thing is the more people who use Tor in your area the less likely they are going to put all of them under this sort of scrutiny. If you are the only person within a hundred miles of where the pack was sent from who is using Tor, you are an easy low hanging fruit. If there are fifty Tor users in the same radius, it will cost them a lot more to do targetted attacks against fifty people to find one person. If they go to this effort or not will depend on how valuble of a target you are : how much resources will it cost to do these attacks / surveillance etc
another thing to take into consideration though is that they are fairly effective at filtering out noise via various strategies. If they identify fifty Tor users in an area they may do other things. How many are on parole? They are easy targets and have little legal rights against search. How many have criminal records for drug charges? How many fit this profile or that profile. This isn't a perfect strategy but its one of their techniques. You would also be surprised how much profiling data is already available to LE on you, if you use facebook you pretty much make your entire social network open source intelligence. Have a lot of friends who were busted for drug charges? I wonder in your extended social network how many people have been busted for drug charges versus the extended social networks of these other fifty Tor users in your area and their social networks. Better call up a datamining company and do some database processing. Or they can add other data points to the intersections.
the intelligence is just to help them narrow in on evidence, see where to best focus their resources until they have enough resources to focus on a target. How much they are willing to put into it depends of course of the specific target. The use of intelligence often will not even come up in court. They don't need to say why they knew to target you as long as they follow the law when they go about gathering the needed information. And some times they are just crazy fanatics anyway and will break the law because they are crusading against the devil as far as they are concerned. Or they are just crooked for whatever reason. I still think the majority of LE are "law drones" though, and will act in accordance with the law, unfortunately regardless of how fucking corrupt the law happens to be. IMO they are just as bad.