I'm not quite sure how sites do it, but, lots of sites manage to enforce the article limit across even incognito and even across browsers... i pasted an archive.is link (http://archive.is/o3LVk) which is quite reliable for me and 99% of the time someone else already archived it.

So that's what those are supposed to do? Everytime I click on one I get an error, currently it's "Error 1016 Origin DNS error". Never actually saw what's behind that site but it does not seem like a working domain.

Are you using Cloudflare's DNS servers? Yeah, it doesn't work with that, for some reason.

Same way scummy ad networks do it (in fact they probably use ad networks' tech), google 'browser fingerprinting'.