My problem is, merchants usually don't show you the search query the web surfer (buyer) used to find their site. So I have no way of knowing which AdWords listing the buyer saw and clicked on. I can add the "?source=adwords" tag at the end of the target URL in the listing, but if the merchant doesn't list that information, it doesn't do me any good.
Am I missing something? Is there a tracking solution out there that solves this problem?