What needs to happen, for the sake of enjoyability (if not realism), is have merchant inventories be level-scaled (including Dungeon-loot table materials), so the player is more than just a supplier of Worthless Expensive Junk.
In fact, level-scaling town loot with dungeon loot is somethign that isn't done enough, and is actually unrealistic if you want a workable believable economy: As you sell valuable stuff to merchants, because they buy it, it means there's a market for what you're selling. By selling unwanted magical arms, armor, and artifacts, you end up outfitting other adventurers (Even if you never see them nor evidence of them, they can be assumed to exist in the compressed 90% of the world), who go out exploring the 90% of the world between the 10% you can play around in. (Watch out people! I take BIG STEPS!), and bring back and sell different loot to the merchants, so there's always the chance of the merchant having something you want or need. ("Heya Mr. Dhovakin, A mage just brought in this magic suit of Ebony Armor you might be interested in). It also allows the shop to sell stuff that's above your level (That Rusty Iron Longsword you sold last month was bought by some farmboy... he came back in full Steel armor yesterday and carrying a Dwarven Longsword... Interested in seeing the Falmer artifact-weapons and Chainmail armor he sold? Or how about this nice new selection of scrolls?)
It would even justify the level-scaling of townspeople's loot as well: The rich and priviledged would want fancy shiny loot, weapons, and armor for prestige, and when you destroy the demand for those 100 Iron Swords you sold last week by bringing in thirty or so Dwarven weapons, the old stuff goes on clearance, and purchased by the lower classes for self-defense against thugs and gangsters who bought that nice selection of Battle Axes you sold last month, and the middle classes would buy those shiny steel swords you supplied so they'd have shiny weapons that say "We're still richer than the poor guys with Iron weapons!"
I love this idea. This is sort of what I was driving at when I mentioned making store inventories and cash-on-hand dynamic, but not in anything close to this detail. I think it would be a great addition to the game.
And I also disagree with the Mercantile experience being monetary benchmarks instead of based on quantity of sales: Who's the better merchant, the guy who someone to buy a 2-GP apple for 5 GP, or the shmuck who sold a Priceless Suit of Heirloom Armor worth hundreds of millions of gold for 25 GP and a feather? According to the "Mercantile should be based on Gold Value" crowd, the guy who sells the armor for 25 GP's the more skilled merchant. Personally, I think XP should be based on either individual sales (As in Oblivion). The guy who convinces a merchant to buy each individual arrow he has to sell does learn the art of trade faster than the guy who just sells everything he has at bulk for a reasonable price. Just think of it this way: What is your character actually saying to get a merchant to buy an item? The solution to Oblivions "Sell one arrow at a time" is to have the merchant's disposition drop with every sale of a non-unique item because you're wasting their time. In addition to making each sale less profitable, once the merchant's disposition drops low enough, they will cancel all transactions and kick you out of the store for the day (once the day's elapsed, the disposition could reset to "1" above the kick-out threshhold). To make up for the occassional forced disposition drop (Making identical transactions in a day may become impossible), each daily unique sale could raise disposition by 1 (Instead of basing it on an arbitrary cash limit).
To clarify (lest I become nothing more than a faceless member of the "Mercantile should be based on Gold Value" crowd), if the game is to either base experience
exclusively on the amount of money that changes hands or
exclusively on the number of transactions made, I would prefer the former to the latter and think it makes more sense. But yes - certainly - experience should be much more complex than that, with some base amount just for making a transaction, more for simply negotiating at all, more yet for negotiating successfully, some for the amount of profit made (particularly if a real merchant economy exists, such that you can buy stuff in one town and sell it in another at a profit), and any number of other variables.
And I love the idea of merchant disposition being dynamic - I touched on that in addressing the possibility of intimidating a merchant into a better price, but I'd like to see much more than that. And the idea that selling the same item one at a time would serve to drive down a merchant's disposition makes perfect sense to me. And in addition to adding to disposition for each unique transaction, I would think it would be possible to add even more for a particularly welcome transaction - however, the game might determine it, if, for instance, you showed up with a load of beer just as the townspeople were starting to complain bitterly to the merchant because he was out of beer, and if further you were to offer that at a particularly good price, that would bring about a huge increase in the merchant's disposition. Or something of that nature.....
Good food for thought in that post - thanks.