Ok, so if the adwords advertiser gets a low ROI, you get smart priced. That comes from http://adsense.blogspot.com/2005/10/facts-about-smart-pricing.html But how is that decided by Google ? How do they monitor the ROI ? That surely can't be monitored by them because in most cases it will be related to a third party. Does it also depend on the CTR? If you have a high CTR (6/7%) are you not going to get smartpriced than if you have (<1%) ? I'm saying that because in most cases, people who say that are smartpriced are those who have a low CTR.
your assumptions are incorrect, i'd suggest using the search feature out here, because all of this has been covered many times.
I think only by geting targeted traffic with converts the best you can avoid the smartpriced but it's just a theory ....