When selling tools, put up what you think is a high price to start with. If there are no takers, you can drop the price a bit next week. Repeat until you find the point where supply and demand meet.
And do the opposite when buying. Start low, and if you get no favourable result, up your bid. But keep an eye on it, because the competition is also bidding and if you start too low the tool might be gone before you know it.