These "freelancer" heuristics are dubious. Despite that fact that 100% of my income last year is printed on one 1099 or another, I satisfy less than half of them. A year ago, I satisfied zero of them.

I use an @gmail.com address because I don't want to worry about getting spam-foldered when I email a new client. I don't have a business license because sole proprietorships don't need them in CA or anywhere else I've worked. I've never furnished my own consulting agreement because every company I work with already has one they're comfortable with. I only gathered the other paraphernalia of freelancerhood after a long period of being too busy with freelance work to do so.

Notwithstanding false negatives like myself, these heuristics might help you identify who among your consultants cannot be persuaded to become an employee. But they're a poor proxy for judging diligence, reliability, or any of the other qualities you should be measuring by portfolio work and references.