There are many nuances that change when it comes to selling an open-source license. How am I to ensure that users can't simply offer my product, with a slight m

There are many nuances that change when it comes to selling an open-source license. How am I to ensure that users can't simply offer my product, with a slight modification, for free? It's not as simple as providing the license on payment. I legitimately have no idea how I would prevent legal forks, ensure proper credit, etc.