It has to be emphasized that Medicare is administered by each state and the individual states have considerable freedom to change many of the policies.

There is, technically, a distinction between "negotiated rates" and "dictated rates," but in most states Medicare sets an amount that is the maximum that will be paid for a given procedure or treatment. The rates set by Medicare are generally significantly lower than what the providers would bill otherwise. Any provider who agrees to accept patients with Medicare must accept the amounts set by Medicare, and can't pass on any difference to the patient or to any other secondary insurer. Medicare will pay part of the amount that they set and the remainder of the Medicare accepted amount can be billed to a secondary insurer or to the patient.

For those not covered by Medicare, and for "secondary coverage" for those with Medicare, group insurance policies usually can negotiate "limits" on amounts that providers who have agreed to accept patients covered by the group may charge. A "large enough" Company that provides insurance for a sufficient number of employees can exert considerable "encouragement" on an insurer to obtain more effective negotiations and better rates for the employee. For those not covered by a company provided policy (with or without partial payment of fees by the employee) public "Group Policies" can also negotiate rates. Blue Cross/Blue Shield is one of the larger group insurers and insurers of this kind can group independent persons into "local" groups and may also be chosen to administer company provided policies as independent groups.

While it may not be typical for other states, a Medicare Summary statement picked at random from our pile (the pile is braced and reinforced to prevent tipping), along with the separate statement from secondary insurance show:

  $ 1,040 billed by Provider
  $   264 Approved by Medicare
  $   211 Paid by Medicare
  $   179 Paid by Secondary Insurance
  $    16 Billed to (& Paid by) patient
  $   264 Total Paid to Provider

I haven't run the numbers to verify, but it "looks about like" most that we see. [$264 Paid / $1,040 Billed = 25.3%]

A Provider who has agreed to accept Medicare may ask you to sign a waiver for something not expected to be covered by Medicare, and if you sign the waiver you may be required to pay full price for that individual item on the bill.

If you are treated by a Provider who has not agreed to work within Medicare and/or has not agreed to work with patients insured by your other insurer(s) the full effect of being "uninsured" may apply. The result of using "out of network" services is USUALLY A DISASTER and everyone (in the US at least) should be aware of what can happen.

Discussion here would be too lengthy to include, but an excellent recent article is recommended reading:

Out-of-network billing is 'out of control,' report finds.

(The article at the link may be most closely related to the original question in this thread, and describes something that can happen to anyone regardless of how "insured" they might be.)

John