Most of the paid plugins I've messed with have code to phone home and prevent operation if there's not a paid license of some sort.

However, before you bother trying to put effort into pirating those, I recommend making certain that what you want isn't already freely available a different way. Many paid plugins have decent open source and free alternative plugin(s) that can be used instead. You just have to look hard enough in the plugin listing. The WordPress ecosystem is vast, but there are a ton of smarmy assholes charging monthly subscriptions for plugins that replicate features provided by free plugins and hoping you won't notice.