Bears repeating! So I did!
The basic law of free market economies are as old as mankind.
If I you have something of value that I desire it is far easier and less costly for me to attempt to barter it away from you with something of value that I have and you want than to obtain it by any other means. It has always been thus and always WILL be thus in truly free markets.
The problem, of course, is that there are darned few, if any, of those to be found.