For sales you will do the best with actual "clicked" traffic. With that said I have made sales with skimmed, blind, popunder traffic as well. Gotta track all your buys and compare ROI to see what works the best for what you are promoting. Buy+Track+Analyze+Adjust=Profit takes a little bit of wasted money to figure out which sources perform the best but over time you should learn from the wasted money if you analyze.
