How exactly does the dual-licensing work in practice? Can you remain the sole seller of exceptions? That is what is to prevent someone else from forking your p

How exactly does the dual-licensing work in practice? Can you remain the sole seller of exceptions? That is what is to prevent someone else from forking your project and then selling the exceptions? I've always suspected that in order to make it in Open Source you have to be highly socially active. (seems like a requirement for everything these days) Otherwise, someone who has more social capital(active forum(s) presence, blog(s), SEO etc) can sell/support your GPLed product perfectly legally and make a good living from it while you starve. Let's imagine a ridiculous scenario: someone takes Firefox, slaps their own logo/branding, maybe makes some minor code changes, maybe not and sells this product (source code is still freely available to this derivative product). This actually has happened before(citation needed). The main difference between your tiny OS product and Mozilla one is that Mozilla has tons of social capital and anyone trying to charge something ridiculous for a Firefox clone would be laughed out of Internet. For example, there were people selling various GPLed products on eBay and as long as source was included there was nothing illegal about it.