Leatherworker -
Don't know if any other professions noticed this. Most of the "expert" trainers I come across have thier patterns "available" but I am only a journeryman leatherworker. So I click on the pattern and pay him to be trained. Some patterns I actually learn, others I don't. But I still pay for the training. So... something is a miss there. The expert leatherworker in Ogrimmar "The Drag" area this is most notable. (by notable I mean noticable, noticeable...whatever)

On Blizzard servers, expert trainers tell you you have a lot to learn before they'll talk to you.  Presumably once you master enough at the journeyman level.

  I found, at least for alchemy, that I can buy up to the artisan level, provided I have enough money.  But the catch is, if your alchemy skill is low, most of the expert/artisan potions will fail until your skill is high enough.