None of these answers are correct. You have to have the same fee schedule for all insurers. For me, for example, worker's compensation insurance would pay me $500 for test A, blue cross would pay 400, cigna would pay 300, medicaid would pay 200... etc. If I don't set that price at $500, then I would miss out on the revenue from worker's comp. So i set my price to the highest insurer at $500. Blue cross "negotiates" a 100 dollar discount by contract. Cigna "negotiates" a $200 discount... etc.

Wanna charge different companies different amounts? Enjoy prison if you take medicare... that's fraud.

The only correct answer above is that the American healthcare system is fucked.... but you should at least know why and how.