Vile of Vile's Golden Auctions has written a good post do-it-right-or-dont-do-it-at-all-tsm.html which speaks of the importance of watching what price you put your actions on at. In summary the lesson is don't just let Your Addon (in this case TradeSkillMaster) do the posting without watching the prices it is posting at in case there are some rogue competitor prices in there.
Personally, I would a step further and suggest you pay attention to your minimum prices. If you set your minimum prices at levels which you are happy to make a sale then being priced low because of rogue pricing will not be an issue. Sure, someone may be pulling down the prices to scam cheap items from you but you will always be selling them at prices you are happy with and, let's face it, you can sit and craft the items all day.
for this and other ideas on the glyph market please follow the link to the free Croda's Inscription Gold Guide