I figure everyone will start out with the basic "play one char, dont buy anything, sell everything you dont need and push content as far as you can". Remember the blacksmith is divided into tiers and the normal mode recipes are very reasonable, I expect for most people to dabble in the low end stuff on their own even if they have no intentions of going all the way with it. So I dont think the market will come into its own until nightmare or so, as people get that difficulty level transitional chill and take their pile of money to market to shore up their weak spot (or whatever other specialized bottleneck the game throws at us: eg the fire/light resistance needed to handle diablo in d2, trying to get past duriel solo etc)

Just be sure to put a buyout on your sale, so they can have it right when they want it and make that impulse buy, instead of leaving them the hope that theyll find it on their own, or worse the bid winding down draws them to realize that their current need wont matter in a day or two.