Don't be afraid to ask for references when dealing with another party. If you don't know what something is worth, there are many places in your phone book or the Internet that can help you arrive at a value. Also, look at other auction sites on the Internet to see what things are selling for. Call around and be informed. When listing an item, be fair and honest in your evaluation.
Many collectors are very particular about nicks, scratches or tears in a book, for example.
Be realistic and do not ask for the impossible. Put a value on your product or service that is realistic and can be verified. If you have a boat , you might exchange it for a car . If you have a 1928 Dodge , you might trade it for a diamond ring for your wife. If you're a scientist , you might exchange your services with a consulting patent attorney .