bijan814 - well here there is another. I get lots of clicks not many sales. Find out where G is placing your ads!!
That's where the quality score became relevant and landing page come into question,quality Score$%$ came into play.
Google says you get clicks and no sales because your product or landing page sucks, I say the traffic from Google SUCKS!
My conversion rate on Yahoo! is incredible MSN not that bad 30% possibly, Google? I forget the last conversion.

Google has less advertisers willing to pay ludicrous fees and many more have figured out their content networks are horses crap to put in nicely have gone away, their core financial base.
Yet they still allow arbiritidge and domains for adwords, if they are trying to fight spam they really got me baffled.
As a matter of fact they seem to be encouraging it, at the expense of the user.

Good Luck Google fan bois real soon you'll be all alone.