Yet, advertisers pay for 100% (or very nearly that amount) of ads displayed--regardless of the client.
Per spider.io, bots are ripping off advertisers left and right. That being said, scared advertisers are the target market for their products.
That means that bots who declare themselves make about 13.5% of requests to this site. The robots.txt has no restrictions.
I don't know if that's helpful.
Bots that don't trigger js, however, are more a drain on bandwidth than anything else.
My company right now won't purchase RTB ads that display outside of walled gardens so that we can 1. manually verify that the ads are showing. 2. Minmize the number of bots seeing the ads (presumably it's hard for bots to infiltrate Facebook or the WSJ than Buzzfeed).