Should a Merchant provide a cash refund for returned merchandise that was originally purchased with a credit card?

No. The card associations do not normally permit cash refunds for any credit card transactions. The only exception to this rule is if the purchase was made with a prepaid card (e.g. Visa or Mastercard gift card) and the cardholder is returning items, but has discarded this card, you may give a cash refund, have a check issued through U-M Accounts Payable or in-store credit.