Sweet, im glad some people see the Gem idea here.
There is another idea, that might be an easy fix to wandering vanishing vendors
Although I dont know how random you can make it this way..
have three-five rooms maybe more a mob/vendor can spawn in, MAke all those rooms the same area, have them not be in areas alreayd.. you know, like crevicies that are hidden, so you could do this well. But they link to rooms outside the area.
Have a rare spawn timer, thats unique like GMA etc. Have a timer when the mob spawns, to delete itself, have the room its in so no other mobs can go in, and so it can't go out.
There for that eliminates the problem of the mob going where it aught to not go.

You could even have it share a timer with a few other mobs, And each vender sells one unique item, maybe even have the rareness of the item, depict the timer, like maybe said npc, only is around for 10 minutes?
Maybe the crappier or un rarer the stuff, the longer it sticks around.
(of course you could always do the wandering around, like inbetween cities etc.. get people back into walking around to find stuff miss so much of the work everyone puts in with people who gate and travel.
ESP with the new augments. If everyone goes for gate, lol they may not really travel roads ever again

This way that mob would be even harder to find. *grin*
Just throwing that out there.
-Sye