Let's see what's waiting for us from the businessmen's perspective.
- All items, except for tradeskill materials used in the BC become more or less outdated and therefore of low price. So it's time to clear up your bags. The lvl70 epics, sellable quest items and such will not interest anyone after the expansion hit the market.
- The next content patch, with inscription will come very soon. Part of it already downloadable, the whole will be here in weeks. So prepare for herb price skyrocketing! Other skillup materials can also start inflating if the BoP tradeskill items in WotLK encourage lot of people to level new skill. If you want to reskill, stock up materials for yourself too!
- It's more or less expected, that besides some really dedicated guilds, raiding will stop. Lot of PvE oriented people do it for the loot (or to be more specific, the assumed status provided by the loot), and they will have the attitude of "why suck at BT if the first lvl 71 mob drops better loot in northrend". Though it will not drop and T6 will only made obsolate by lvl80 blues and first raid epics, this is the common attitude. So if you are mostly serving raiders, you may have to find another field.
- WotLK will open a new and strange market: lvl 70 twinking and skillups between slvl 300-375. This won't be a big business in the first months. Most people have proper skills and lvl70 gear. But 4-5 months after the expansion is out, new players will reach lvl60 and will need quest and repu items for powerlevelling, tradeskill items to reach slvl 375, gear to be twinks, items for BC-related archivements. Karazhan, ZA, BT will be just as empty as Solomonce, BWL and An'Quirai today, so they will buy such items. If you have a lot to invest and like this millieu, it's time to stack up while such items are available in great quantities.
- It is probable, that lot of tanks and healers will respec for DPS in order to maximize his levelling potential. They will possibly buy enchants and BoE gear to their new spec, so it's an opportunity to sell affordable mid level enchants and items for them.