Competitive ads and services

This isn’t about your competition; it’s about Google’s competition. Like any
good contender, Google doesn’t want competitors competing for its share of
the prize money. So, you can’t display ads from any competing services that
could be confused with AdSense ads.
For example, it’s okay to include ads on your site from Amazon or other retail
services. And you can even include other pay-per-click ads, as long as they
don’t mimics AdSense ads. Ads that look like they belong to AdSense but do
not are a real no-no — that could really stir Google’s pot!
Google stops just this side of saying you can’t use other advertising services, but
only because denying your freedom to use any program without thought of how it
could be misconstrued as a Google capability is creating a monopoly. And monopolies
draw the attention of Big Brother. He’s a sibling no one wants to spend time with.