Users running a PPC Campaign in the Google AdWords platform are given the choice of displaying ads on the Google Search Network and/or on the Content Network.
I have never been a big fan of advertising on Content Networks, as I
find the automated matching process to be less than ideal. I can
generally browse the net and quickly find ads that are irrelevant to
the sites they are displayed on. This can give one a healthy dose of
skepticism.
<br/><br/>While advertising on Content doesn’t generally cost
a great deal, we have never seen much in the way of results. By and
large we do Search Network only, however recently I have had to
re-assess that view.
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Increasing Conversions with AdWords Demographics