What if the seller of the Hillary book quite deliberately targets democrat keywords to put his book under your nose on purpose?
It's not necessarily that easy. I've targetted an ad for a specific (relevant) location, and it took me a half an hour to find the relevant keyword/creative combination to get in there- an oddball keyword phrase that I wouldn't use otherwise.
But I see your point.
I would prefer to see it from publisher AND the advertiser side.