Keep an eye on the prices of the items you are posting, even when they are posting above your minimum price (which all items will do so if you have your posting addon set up correctly!)
There are times where the cheapest glyph on the Auction House (or any item) may be a large amount lower than the normal price or indeed other glyphs posted at the time. This may not be a concerted strategy by an aggressive competitor but merely a normal player selling an item at a random low price.
In this situation don’t undercut the glyph (you don’t want to reset the market price at this level) but either don’t post at all or post higher up the undercut the other glyphs at the higher prices.
You can best see what prices the glyphs are posted by pressing "Show Auctions" on TradeSkillMaster before you press the "Post" button
Of course, if the posted glyph is below cost then buy it!
for this and other ideas on the glyph market please follow the link to the free Croda's Inscription Gold Guide