Typically the items sell for the most in the early days of the patch, but you also pay more for materials. Doesn't always pay off, but the crafted stuff is better ilvl now than in those early days.

I would recommend being wary about making a large investment on an item that there are already several of on the MB. If there are too many people selling for too high and the demand isn't there, it can be whoever wins the undercutting game.