You can see people coming through to your site with Google in the Referer, or the referring site in the Referer, or some other random rubbish depending on browser, OS, and day-of-week. You get a real mixture.
I would not be at all surprised if only ~30% of the Referer values showed the hand of Google. Is that how you were attempting to detect it?
Note also that if people get a slow response they may cancel their clickthrough LONG before your Web server sees anything, eg because of poor DNS or network connectivity.
Rgds
Damon
That is not a good deal for us. I haven't had any business from my six week trial. Granted my product is expensive and the field is crowded, but none of my visits ended in a sale. I paid $2.69 avg. per click. They say 1500. I show 569. Would you pursue with Google?
The numbers you give look plausible to me, especially adding in Matt's cache factor.
I have no reason to believe that G would be telling porkies, but you might ask them to (re-)investigate if any of the clicks look suspicious, eg from a competitor's IP address or one of the egregious "paid-to-surf" sites.
If so then you may (a) get a partial refund and (b) be able to better target/filter your campaign in future (eg adding to your excluded sites list).
Rgds
Damon