Also, why do I see the same ads on 3 or 4 pages and then on the 5th page it changes to different ads?
Thank you.
The sudden appearence of new ads on later pages could be caused by advertisers with a limited budget that doesn't allow their ads to be displayed constantly. Google spreads their impressions over the day, so it is possible to have have several rouns of impressions before seeing the ads.
Another possiblility is that there really are a lot of ads and all the first 4 pages are different ads, but just phrased the same. I've seen some searches where all the affiliates for different or even the same company write almost the same ad copy. Add in the dynamic keyword insertions in titles and expanded broad match and some searches produce repetative "junk" ads. If I even see a third of the ads on the first page like this I'll usually ignore the whole group and concentrate on the natural SERPs because I've found that the ads in these cases are pretty much worthless affiliate pushers instead of real sites.
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