In my state (New York) balance billing is legal as long as you do not participate in an insurance plan (Medicare excepted - see below).
For example, I see a patient in the office as an out-of network patient (i.e. I am not participating in their insurance plan). My bill is for $500.00. The insurance pays the patient $400.00 - what they “allow” for my services. Because the patient has the contract with the insurance company, not me, I legally bill for the balance of $100.00, and the patient is legally bound to pay it.
Now, if I participate with the patient’s insurance, I am legally bound to accept the insurance plan’s payment (of course, if there is a deductible or a co-pay, the patient must pay that).
Medicare is different inasmuch Medicare limits what a doctor can charge for a given service. So, of my usual $500.00 fee, Medicare my say that I can only charge $250.00 - so I write off the other $250.00. Of the $250.00 that Medicare allows, most plans pay 80% (unless the annual deductible has not yet been met). Medicare requires that I bill the patient for that 20% and any deductible, and the patient is bound to pay that, either out-of-pocket or by secondary insurance.
Moreover, Medicare requires that a patient sign a waiver at every time of service, indicating that if Medicare rejects a claim as being non-covered, that the patient will be responsible for the bill.
This applies to things like Travel consultations and immunizations - if I don’t get that waiver signed, I cannot legally bill the patient for the consultation, and any vaccines administered (yellow fever, typhoid, polio, hepatitis A, etc), even though I have provided the service in good faith.
Medicare rules apply to all beneficiaries, no matter their income - the pensioner on a fixed income pays the same as the retired CEO with 5 homes and 4 cars.
Bump
Let me ask you this. You bill my insurance company, lets say Blue Cross Blue Shield, $276.00 for services to me. Blue Cross determines that the allowable amount is $166.00 They then pay you $149.00 and I pay my coinsurance of $17. End of story.
Now let me ask you this. Lets say I don't have any insurance coverage at all. Are you going to bill me the same $276.00 or are you going to bill me the $166.00 which is what the insurance company would normally have paid you ?