I once visited the site of a 'trading' personality who was selling a football system. Incredibly he had his customer spreadsheet exposed on the site, accidentally I guess.
I had a browse of it. He had earned £290k in sales and paid £60k to affiliates. The name address and details of every customer and their full details and the affiliates were listed on the spreadsheet.
So it's just not a duff system you are buying, but you are giving your details to somebody who probably doesn't care much for privacy or what happens to them one they have them. Alarming really.