Lot of different tricks. One example: just by using a Google Bot user agent some websites will let you access the full content. Sometimes working with some cookies, blocking some particular 3rd party JavaScript libs, some other are more complicated.

Perusing this file here - https://github.com/iamadamdev/bypass-paywalls-chrome/blob/ma...

It removes the popup elements that cover the page and other little tricks.

The common key thing across all of them, though - the server is sending the content, and then a little JS payload that creates the popup asking you to pay.

It's not a particularly good way of protecting the content of the article, for obvious reasons.

Usually #3. Or corrupting whatever the site uses to run its “5 free articles per month” counter.