At work we have a scraper that likes to use a particularly expensive search query using hundreds of different ips dozens of times per second, all so that they can scrape data that is freely available from us as an XML feed at a different url.

Every time I found a way to fingerprint and block them, they'd change their bot to avoid detection. Captcha for rate limiting seemed like the least bad option.

However, eventually I decided that instead of blocking them, I'd return random results from the db. They weren't checking the data too thoroughly because to this day they haven't changed the bot to avoid my most recent pattern detection. They're still merrily scraping useless data.