If you have rare resource items, do not complete a tradeskill quest of the same type (ore, rock, roots).
Example: I had a fir branch today, tier 2 rare item from forestry in the Steppes.
I went and finished my wholesaler quest for severed ash, and it took my fir branch.
Watch out and be careful with your money, or else you'll be pissed and generally unsociable like me.