I don't think it's unreasonable to give a portion of the check in cash and the remainder in another cashiers check. Then set up an appointment for the client to return to get the remainder. We don't have any obligation to clean out our vault cash for anyone, even a client. I had a client get very angry in a similar situation, and ask, "Aren't you a bank? Why don't you have the cash on hand?" He didn't understand that we didn't actually make the money - and that we had to have it available for other clients.
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Opinions are mine and never to be taken as legal advice!