Tell this to guys from Transtrend BV or Meyer Cap. Mgmt "your backtesting is useless". They'll have a nice laugh.
Reasons why someone would sell a system? 1.) Getting an amount of money for it that is currently considered a large amount by the seller. 2.) Scam. 3.) Can't think of any other reasons. For myself it is number one, I consider $200,000 a large sum of money, therefore I would sell the program I developed for that amount. Of course eventually as my portfolio multiply's I would never sell it at any price. Tired of trading is a weak reason, how can you be tired of trading profitably?