There is certainly a difference between a list price and a negotiated rate, but there isn't some sort of secret "we'll tell the patient in writing we're paying $400, but actually we'll pay you nothing" rate.
That’s insurance based healthcare in a nutshell. Insurance doesn’t negotiate just rates but the actual reimbursements.
The real fraud is the fact that insurance companies have been buying up health care practices/hospital systems and dropping all other providers from their networks and forcing the patients to go to the insurance owned providers (often times unbeknownst to the patients). Although there have been a couple successful large class actions by both doctors (who got dropped) and patients as well, but this hasn’t changed anything in practice just provided a little hush money.
There is certainly a difference between a list price and a negotiated rate, but there isn't some sort of secret "we'll tell the patient in writing we're paying $400, but actually we'll pay you nothing" rate.