Many hotels require the security of a credit card to check in, but will allow you to settle your bill with cash at check out. Perhaps you can use your card to check in and settle your bill with cash and this will satisfy the shop requirements?
This site has somehow broken the chain of this thread. Am jumping in to say GO BACK TO THE GUIDELINES for your shop. Maybe a cash integrity issue is the angle and you are asked to inquire or actually offer cash. We don't have all the details but extensive hotel shop experience is that we MUST pay by Credit Card or Debit card. This is the only way the hotel will reverse the charge for some MSC.