Code 73s are Accounts Receivable claims filed when Walmart has made multiple payments for the same goods/POs. Walmart is requesting payment from the vendor to reverse the additional payments they made.

Since a valid code 73 is the result of a mistake by Walmart, there is not much that a supplier can do to prevent it. 

Yes, if Walmart is claiming to have made a duplicate payment but you have proof that the payments they are referencing match up with real invoices, then you can dispute it in Deductions Navigator.