[talldayo]

Too many ways to count, really. It's an enormous system and I'm not qualified to explain it in detail, nor am I a customer of their products.

The long-and-short of it is that Google wields undue monopoly power by mediating their competitors in online advertising, and abuses that control to manipulate ad rankings and kneecap paying advertisers. They do this in several ways, like changing the font/frame/location of the advertisement and fixing it's ranking relative to Google's own products. This is the main argument against them, though there are tons of little inconsistencies that many highlight as salient.