I set my fallback price at 400 gold.
I do this for a number of reasons.
1. It resets the glyph price to 400 gold when all are sold out – and so starts the undercutting cycles from a high level.
2. It sends a signal to my competitors that i am willing to sell my glyphs at those prices and hence perhaps they should join me. I give the impression of being a sensible competitor. That is key. A market participant with the reputation as a rogue competitor receives more focus. Furthermore, other market participants that have lower fallback prices become tempted to reset theirs higher as well. Should this occur then the profits from the glyph market rise for all.
3. A customer that comes to the Auction House to buy a glyph that is sitting on my 400 gold fallback price knows that the only way it will come down to its normal price (and lets assume that was 150 gold) is through a few days of undercutting or if another market participant has a lower fallback price. I normally find that such customers just bite the bullet and buy the glyph. Glyphs are considered capital items. i.e. a one off purchase for use in perpetuity and therefore customers are willing to pay more than for say useable items like potions.