I don't know why this comment is downvoted, it mirrors my experience. I'm responsible for a few domestic high traffic websites and have done some analysis from log files to find suspicious traffic, i.e. user agents saying they are chrome but not loading images or css files, having many page views (i.e. 50 where our average user has 2) etc. It wasn't foolproof but the false-positives where < 10% in my random checks. These bots made up ~10-15% of page views.