I work on a fully open data repository. The website has the API linked in 3 places, so when I find inappropriate scraping I block it with "HTTP 420 ... see <API link> or contact <email>".

Some people probably switch to using the API, but no-one has ever contacted us. They either give up, or run their scraper on a different computer -- I've seen the same scraper move between university computers, departments, then (in the evening) to a consumer broadband IP.

I really don't understand why anyone would bother writing and using a web scraper when an API exists. Does the API not provide all the same data/functions as the website? Scrapers are a big PITA compared to just using an API: they're much harder to write to be reliable, and they can break at any time, whenever the site makes even the smallest change. APIs avoid all that mess, and make performance far better too (on both sides), since you're only downloading the data you want, not a ton of Javascript and HTML that you don't.

APIs are often not as complete as the web interface, since the customer sees the web interface and normally the customer is what drives the revenue model of the company.

If pages are driven via an API, then the API is preferable, but publicly facing websites are often a mix of server-side HTML generation and API enrichment, for caching if nothing else.

In that case it seems that the webmasters complaining about scraping need to make sure their APIs actually provide access to all the same data, if they want people to use the APIs instead of scraping.

If the scraper contacted the client, said what they need the data for, and (probably) paid for api access, then my client would probably go for it.

My client is under no obligation to make access to this data easier. It's not really their data either; the information is property addesses, owner names and addresses, and tax assessments and payments. My client wouldn't want to make it easier for scammers to get that data. So they're not going to do anything unless they know the scraper is legit. If that's the case, the api would require authentication, and any fees would be for the server load, not the data.

probably, but as GP said, "The operator of the botnet has NEVER tried to contact my client to ask for an efficient api to access the data"

Some people just don't care for the commons

For what purpose? That’s like suggesting that if people keep jumping your fence and trampling your roses because it’s a shortcut to a public park (in this case, the county records office) that already has public access roads, that you should be obliged to build a sidewalk through your garden, at your own expense, when the real answer should be that the public road should be improved.

If your goal is to get your roses to stop being trampled, it's probably easier to install a few pavers than to spend years petitioning to get a road built.

The ideal answer and the efficient answer are not usually the same.