If you click "Yes" on a request where the max cost is lower than what you charge, and if both libraries checked the box to use IFM, you will receive the following message:
"You are about to supply a requested item with an IFM charge that exceeds the Borrower's Max Cost.
The IFM payment will not be made if you update this status to Shipped."
If this was a mistake on the borrower's part, they can resolve this issue by editing the max cost and saving the request.