Erm, yes.
That's for you to figure out based on past price history, current server market trends, and knowledge of the supply of other goods.
Why bother quibbling at -10 gil? Lower that price by 1k, if not 5k or 10k. If that price is not worth it to you, don't even bother selling the item and move on to something else. Eventually there's a point where it's not worth it to sell at a lower price than is economically feasible for you. If that happens to be lower than your competitors, great. If not, just move on and wait till that item is hot again.
If you thing you're getting shafted because people are selling stuff at a much lower price than what you want to sell it for, then news flash: it's probably not worth as much as you think it is, and just because it may have cost you a lot of gil or time to gather/make, that doesn't mean that it cost as much to someone else.
