Some of those mods on BTB's list change this aspect of the game. One of them disables the Barter function on Creeper and the talking Mudcrab. Another one makes training much more expensive, so that you basically only use it if you're one skill point away from advancement in a guild or something. I don't really remember right now which does which, but I made a post earlier in this thread summarising a bunch of mods:
http://www.rpgcodex.net/forums/inde...r-morrowind-thread.85809/page-14#post-2926053
It stands to reason that you can't just go around selling artefacts at their full price. That's why they're artefacts: they're essentially priceless; their value is such that some small-town merchant in backwater Morrowind could never just go around buying them up. The greatest ones, according to Yagrum, "have been seen, owned, and lost, again and again throughout Tamriel. Some may be myth, others may be hoax, but regardless, many have lost their lives attempting to find or protect these very coveted items." Not the kind of stuff you'd just buy off of some random adventurer to display in your store front.
Of course, with walkthroughs, UESP, etc., everyone knows where to find all the artefacts, and everybody knows where to find merchants that are basically Easter eggs and how to get the most bang for your buck from them. So preventing this option makes sense.
I still think the surcharges are an inelegant solution to faction services, though.