I would think it would be very difficult to meet the requirements of dispute resolution if your institution knowingly assists a customer in giving access to a non-account owner.
For example - We would question a customer who wanted us to dishonor a withdrawal made by someone who they "loaned" their card to but took more than agreed - your situation could make some of those examples a common thing. Who would file the EFT Inquiry? The account owner who didn't do the transaction? The card user who hasn't signed your signature card and agreed to the account rules?
I would pass if I were you.
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Randy at Washington Trust