I was mocking the use of the term "scam" just because you don't get their business model. Everything about them and how they work is publically available and easy to understand if you have something greater than a 5 second attention span.
https://www.flexjobs.com/faq
There's plenty of ways to apply for jobs out there, and FlexJobs aren't even the only job curator out there. But hey, go try out some different methodologies and see what works best. There are no guarantees in life.