If you're selling things at auction, in your tower or at marketplace, you may find it helpful to check what price you can get from the item elsewhere. I have seen some things for sale at auction recently that are well below what the Tool Vendors will buy it for. Then when you add the auction fees, you are getting even less. I'm not saying that I don't like buying things cheap but I made that mistake when I was first selling things so it seems fair to let people know.
I put this in general intentionally because some people may not know about marketplace.