Vendor Master Management re: Insurance Carriers

My organization recently started accepting payments from
Medicare and other third-party insurance companies. Our current
policies and procedures for maintaining the vendor master files require
us to obtain a W-9 from the vendor in order to properly identify them
using their Federal TIN. We also verify that the vendor is not on any
excluded/debarred lists from participation in federal health care
programs. In the case of insurance companies, we don't pay them for
goods or services, but rather receive reimbursement for our services.
When the insurance companies overpay us, we must issue a refund so they
have to be added into the vendor master for that purpose.

The ability to identify a vendor by its TIN so that it isn't
inadvertently added as a duplicate vendor is a big concern and I am
being told by our patient financial services department that obtaining
the W-9 from the insurance companies is an arduous task. We really
don't have any leverage over the insurance companies to require they
provide us with their TIN as I believe they can legally take back the
funds electronically if we fail to issue a refund within a certain
amount of time after receiving their request. How do other healthcare
organizations manage the vendor master file with regards to adding these
insurance companies and what requirements do you currently have in place
as a standard practice?

Any input would be greatly appreciated. Thank you!