Earlier quoted context omitted.
"Unfortunately, if you're scraping some data that only has one authoritative data source, they'll know you're scraping them even if they can't distinguish your individual requests from the general traffic." How would they know you're scraping them? Surely the capability of any given website admin to detect a particular scraper would depend on many factors such as whether they're even looking for scrapers or are techn…
They know you're scraping them because their site is the only source of the data you're scraping. The most common example here is airlines. Airlines that haven't agreed to be included in fare aggregators often have their booking information scraped. Even if your traffic blends in, they know that you're reading out fare data from them, because where else would you get it from? This is especially true if you follow it…
Not every scraper has publishing or using data in a detectable way as their motive.
For instance, I sometimes scrape a website to make an archive of it for my own personal use. I never publish the results or use them in any way that the website owners would ever know about. So the only way they could know that they were scraped is if I left some kind of scraping signature while scraping (such as scraping from a single IP and doing it quick enough to pop on their radar or perhaps regularly enough -- ie. without random waits between request, etc).
What you're talking about is probably mostly a concern to people/companies who are somehow making money from scraping data on other people's websites.