Here's the thing and maybe where you're having a disconnect between gross and net...
You will only ever make any real money by selling items crafted from rare harvests (master crafted items) to other players and even then, there is no guarantee that your merchandise is going to sell quickly or at a healthy margin.
To make the waters even more murky, you will find that even if you can make great money selling certain items in one tier, there is no guarantee the corresponding item in the next tier will generate any sales at all!
I'll give you an example using my lvl 69 tailor;
When I was making rare T3 leather armor I couldn't find or buy the pelts fast enough to cover the number of complete sets I was able to sell... As fast as I could make them and put them up for sale, they sold no matter what price I put on them... it seemed like being a tailor was a license to mint platinum! Meanwhile, rare T3 cloth armor seemed to sit in the sales container even if I priced it lower than the cost of the raw materials!
Flash forward to T6 and I couldn't give away leather armor to save my life while cloth flew off the shelf faster than I could find the roots to make the items with!
And now that I'm in T7, it's anybody's guess what will sell or when... I might sell nothing at all for a couple weeks straight and then BAM! 15 or 20 pieces over the course of a weekend at an average cost of a plat each.
My point is that you can't assume that any craft is a short road to easy money... there is no sure thing but for what it's worth, Jewelers have as much potential as any other crafting class and more than most!
BTW - when you get to T6 & T7, you will be able to make a steady income from the sale of full sets of resist jewelery - earrings, rings & necklaces made from common harvests that add large resists to specific damage types for raiding toons.