Why is it so profitable to sell Glyphs? It's easy, on most servers it won't cost you anything to craft them ... Let's say that you buy a stack of Adder's Tongue / Lichbloom / Icethorn for 15 wow gold, you will get an average of 12 Azure Pigment and 4 Icy Pigment out of each stack. That's 2 x Snowfall Ink and 6 x Ink of the Sea ...

Snowfall Ink is used to craft a few high level items, the Runescroll of Fortitude added with Patch 3.2.2, and Northrend's Darkmoon Card (I'll talk about that later) .... and usually sells for something like 10G wow gold at the AH. Yes, you just got 20G worth of Snowfall Ink out of a 15G stack of herbs, and the 6 x Ink of the Sea are a "free" bonus.