Pretty good article talking about Gross Profit and FCF.
The trick, I think, is to wrap your head around the cost of revenue or cost of goods sold line item in the income statement and think about what is going on there. If it is very little to no effort, and largely just an accounting entry, then you may have a “low margin business” that is actually a high margin business. On the other hand, if it is a lot of work and capital investment to produce those margins, well then what you have is often a low margin business.”