1) Only a fool pays per impression for ads on websites. They are even easier to fake than per click ads. Only a bigger fool would sell ads based on what an advertiser tells him the response rate is based on his sales. So even though per click sucks, it's the best of bad options.
Yes, you'll want to do your own internal sales tracking on your own website. That will let you work with vendors who are better for you. But never make the mistake of thinking any of your payment options are good, because they all suck.