The whole point of trading is in the value each person places on BOTH items!
The difference in value is called "haggling", the same thing you do when you are trading cash for a gun! If you traded a gun and regretted the trade, you would probably have regretted selling the gun also, unless you sold it for much more that the actual value. If you don't like haggling, don't trade, and never get into a 3 way trade! Been there, done that!
jcelect