We had a former Google Maps PM give a talk about building APIs, and he addressed scraping. Something he pointed out is that the traffic pattern from scrapers differs from regular users. Regular users make requests for the same things often. Scrapers usually only request any given item once. The really obvious ones do it in order from the beginning. He had a hilarious map showing the requests of someone requesting business information starting from the top left corner of the map. They got really good information on all of the businesses between the North Pole and Greenland before being blocked.