What happen to the claims if accept assignment is not marked in participating provider claims?

Processing Claims for Services of Participating Physicians or Suppliers by Carriers 

The participating physician or supplier submits any claims for services furnished by the physician or supplier, except in the limited circumstances specified in §30.2.8.3 or §30.2.16.  (The exception concerns situations where the physician or supplier accepts, as full payment, payment by certain organizations.)  When an unassigned claim is received from a physician, the carrier must verify that the physician is participating.  The carrier processes the claim as assigned absent clear evidence of intent by the physician or beneficiary not to assign.  The following message must be printed on the remittance advice:
We believe you inadvertently submitted this claim as unassigned.  As a participating physician, you agree to accept assignment on all claims.  We are, therefore, processing this claim as assigned.

Any Form CMS-1500 claim where the participating physician or supplier checks either the assignment or non-assignment block or fails to check either block, the carrier must treat it as assigned.

Where there is evidence of clear intent not to assign, the carrier must deny the claim.  Use MSN 16.6.
“This item or service cannot be paid unless the provider accepts assignment.

Carriers must identify and track assignment violations in the event sanctions must be imposed.

No Part B payment is made on a claim by a participating physician or supplier to anyone other than the physician or supplier (except in the case of court-ordered assignment to other parties under §30.2) even if the beneficiary has paid part of the bill.  However, if the physician or supplier collects any charges from the beneficiary before submitting the claim, he/she must show on the claim form the amount collected.  The carrier refunds directly to the beneficiary, to the extent feasible, any over collection of deductible and coinsurance.  The physician is responsible for refunding to the beneficiary any over collection not refunded by the carrier directly.  In these latter instances, the carrier advises the physician of his/her obligation to refund any over collections to the beneficiary.  Also, the carrier advises the beneficiary of the amount of any refund due from the physician.