You have an existing customer who has appointed an attorney-in-fact? You want to turn the attorney-in-fact down as an authorized signer based on a report provided by a negative data base, aka a consumer reporting agency?
The attorney-in-fact is not applying to do business with you; your bank has no right to run his name/TIN through a consumer reporting agency unless he or she has given you written permission to do so.
There is a huge difference between refusing to accept the POA (the document) and refusing to accept the attorney-in-fact (the person empowered by the document).
In this world you must be oh so smart or oh so pleasant. Well, for years I was smart. I recommend pleasant.