Interesting thought, though in some aspects of the game, you already have vendors charging more as almost a convenience charge.
Vendor prices already do differ from one type of vendor to the next...if you get an earthshaker from Helga, the Liquor vendor, it is regular market value. If you get them from a Mining vendor, due to the convenience factor they are about 3-4 times as expensive. Actually, from what I can tell the Mining vendors also charge 50% or so more for the tools than Hardware vendors (haven't done a detailed analysis).
Guess I've not seen a player congestion yet have an impact on getting access to a vendor. Even if there are 10 players at a vendor, I can still click on it and go about my business.
Fair enough RG...I will admit, that I thought the vendor pricing would be a bit more complex than it is...not just based on the type of vendor, but potentially based on the region as well...the groceries vendors in the meadows are cheaper than the grocery vendors in Alakol...which would cause people, who cared, to shop from location to location to get the best deals. However, it appears they are just by type for now. Maybe it is something they will implement in the future to create migratory travel by the players...I suspect though, many players don't pay that much attention to the details like that, and just go to the same places out of habit.