I always suspected that some of the claims of Gevlon on how easily he was making thousands of gold were exaggerated. But being a man of science, I set out to test it. I followed his instructions on how to get filthy rich in WoW by selling glyphs for several weeks now, and here are the results:
On the positive side I made a lot of gold, my total wealth is up from 30k before to 70k after, and in addition to that plus of 40k gold wealth, I also spent about 10k on various things, like tradeskills for alts. So I'm counting 50k gold made with glyphs.
On the negative side, making those 50k gold took longer than you'd have expected from Gevlon's description. For example my glyph selling alt alone, who does nothing but empty his mailbox, scans the AH, and then posts the glyphs using Gevlon's undercutting strategy, has already 70 hours of /played time, and is still level 1. I don't have an exact count of how many hours my inscription toon spent, but I'd say it was at least another 30 hours.
So that is it, I made 50k gold in about 100 hours, a rate of 500 gold per hour. That isn't counting the time and money I needed to get the inscription skill to maximum and learn every single glyph recipe in the game. Now many of the hours spent lets say scanning the AH or posting hundreds of glyphs were semi-afk. But doing that still prevented me from using those hours for other activities, like leveling alts, or doing heroics and raids.
Now 500 gold per hour is not a bad wage in WoW. But inscription isn't the only activity that nets you that much. For example farming mats, that is either gathering herbs or ore, in Northrend can easily also make you 500 gold per hour. You might have some bad days, where you find very little frost lotus or titanium ore, but on average 500 gold per hour from farming is quite doable.
Now Gevlon despises farming, but I'd say it has its charms. Flying around and gathering materials is somewhat more active than standing in front of the AH or mailbox. And it is more sustainable: You will make less if other players are gathering at exactly the same time as you, but demand is high enough to support a large number of farmers gathering materials at different times. The glyph market is far more sensitive to competition, it only takes 2 or 3 greedy goblins to drive down the prices. MMO-Champion having published a glyph-selling guide while my experiment was running certainly didn't help my profits.
I am currently winding down my ink and glyph inventory. I found the experiment fun, but only as long I was figuring out all the details and tricks of the inscription business and AH "PvP". But I'm not really motivated to spend another 100 hours making another 50k gold the same way. What would I want that gold for? There is nothing I could spend it on. Ultimately I gain more if I spend those 100 hours on lets say leveling one of my alts to level 80. If I see glyph prices going up a lot, I might just jump back into the market again. But right now, with 5,000 out of 15,000 auctions on my server being glyphs, there is too much supply and too little demand.