I am selling premium GPL WordPress plugins and themes. I recently discovered this is legal and jumped on the bandwagon. I originally came at it as a web designer who needed a more affordable way to use premium plugins for my low paying clients.
I always feel like the classic business model is email marketing.
It's the core of any online business. Creating a Lead Magnet and having a follow up sequence that gets them to convert to a Trip Product (which means that they have spent money with you) then I optimize that follow up sequence which is usually 5 emails long. The product doesn't cost much (I don't make much profit on it) it just lets me know who the buyers are and who they are not.
Then after that is fully optimized I go ahead and build a much bigger premium product that I offer as my high-end product to those who've only bought my trip wire product.
After the high-end product I always have an upsell as something they can get to become a "platinum member". This is where all the money is. Most people just focus on optimizing the campaign to get their customers to a trip wire product. The trip wire product should just separate the customers who are willing to spend money with you and those who do not.
I always like to hire a CRO to come in and optimize everything then after everything is optimized I ramp up the marketing.