I redirect all my sponsor hits thru a php script. The script does basic counting and also gives me the ability to quickly route selected hit to a different sponsor.
Many of my sponsor only show second-page hits. The ones that show first page - I get varying results with respect to counts matching.
As long as they are within 10% or so, I chalk it up to slop. Much more than that and I might redirect somewhere else.
One of the most interesting revelations is to see which banners/text people actually click. Have had a couple surprises there
