What DieAz says is wise and true.... the store will only give you a fraction of the items value..
example, I have a Level 7 Short sword 5-6 damage with +1 damage, the Weapon store will only give me 260 for it, I paid more than that, but not much more because I bought it in the Market. There are only so many weapons available in the store and right now there are no level 7 short swords available. There is only one 5-6 short sword in the market for 846 - supply low, demand high, I could probably sell it for 600 easy. I made over 1800 gold yesterday selling of some level 3 stuff, boots, gloves, a trident. I look at what everybody is asking for their stuff then price mine about 100 gold less, cause people usually sort on price to find cheap... The only thing I sold back to the weapon store was a 2-2 Short sword I started with, for some reason I couldnt drop it in the market