People who walk by a mailbox on their way to work will do so in a non-random fashion. Every time they go to work they will likely take the same route and pass by the same boxes. Vendors tend to ship from random boxes that are not in a predictable path. If vendors ship from the same set of boxes, or boxes in a certain restricted geographical area, they will be making themselves much weaker to focused surveillance operations. If they use random locations to ship from, then they will make themselves much weaker to the crowd intersection attack I mentioned above, because people who are going to work do not display so much randomness in their path over time. Another thing to keep in mind is that people who are going to work are going to show up as going to work. People who drop off packages and then go home are going to show up as dropping off packages and then going home. Remember that they can position your cellphone. So it is actually very easy to filter away the noise. Anyone who carries a cellphone with them while engaging in illegal activity is just begging for trouble. Or they could just get records of who all in an area a vendor is known to work out of uses Tor, and use that as their initial crowd of suspects. This is why it is a good idea to use bridges. When manned surveillance is carried out generally is determined by a balance of two things: importance of target identification and target crowd size. If they have reason to believe that one out of a hundred people they have identified is involved in selling small amounts of marijuana, there is no chance they will put each of the suspects under manned surveillance in an attempt to identify the actual culprit. If they have reason to believe that one out of a hundred people they have identified plans to detonate an atomic bomb in a major city, you better believe that they will all be under intense surveillance. It is a very good suggestion. Of course people should not carry cellphones with them while engaging in illegal activity! They are tracking beacons for fucks sake. Law enforcement already have covert cellphone positioning networks and don't even bother asking providers for geopositioning records anymore: http://www.technewsdaily.com/4537-embargoed-law-enforcement-tracks-real-phones-phony-cell-towers.html analyzing that data and carrying out intersection attacks based on known positioning data that anonymous vendors have been in (ie: near boxes) is a serious threat to vendor security and not at all a wild goose chase. It is a serious attack with a lot of potential to fuck those who do not defend themselves against it.