When you say you are anticipating the return, have you been notified by the paying bank or agane that tehy are returning the item for improper/missing endorsement? If you have been notified, then yes, you should notify your customer and withdraw the funds from their account, or place a hold until the item is returned. Notification to your customer as soon as possible should be done. Additionally, you should get the returned item back to your customer ASAP.
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Providing alternative truths since the invention of time