Enhanced bidding is a special feature restricted to Google AdWords that gives AdWords the flexibility to actually make changes in your bidding in order to positively influence your conversions. Enhanced bidding lets you pay as much as 30 percent over your set keyword. It takes the best out of both CPC and CPA, although it does get a little costly in terms of cost per click. Although useful in a lot of ways, caution is to be exercised while using enhanced bidding as a number of marketers have faced unpleasant experiences with cost per acquisition bidding with AdWords.