The reason this is a thing is that other people can bid on your product (Amazon has an entire sponsored product category for this reason). So the reason for Seth Godin to bid on ads for "Seth Godin The Knot" is to try to crowd out other people bidding on the same term (eg another book on the same topic). Can be smart but you don't have to play this game if you don't want to, and the ACOS will tell you if it's worth playing. Even if you don't bid on those ads your own product will be the first result. It's just whether you want to bid up the price for competitors -- if you don't bid on your own product someone else can come in and buy the ad spots cheaply.

Hopefully Seth's publisher knows this?