Put a price tag on it. Successful bartering must result in the satisfaction of both parties. This can only happen if the items bartered are realistically valued. If you have an item you would like to trade, obtain an accurate appraisal. An item is only worth what someone is willing to pay for it. Therefore, do your research and look at the "selling" section on eBay to find out what online buyers have paid for similar items.
For instance, each time Apple releases a new version of the iPhone, the second-hand market for older versions of the iPhone enjoys a flurry of activity. However, you do have to be as careful with the barter of used goods as you would be with the purchase of used goods. Be sure everything is in working order and shows no signs of significant damage.