The problem is that the next guest will also want a refund, labour day or not. Rustling in the night... Buy traps galore, take the opportunity now that the place is vacant and trap the hell out of the place. Peanut butter, chocolate, yummy almond biscuits, whatever works for you. A trap every metre. Skirting boards. Under the bed. In kitchen. In bathroom. Get that mouse/mice! Check where they get in and stop any future ones. Guests will always be able to cancel if there is evidence of mice. Don't poison, it takes too long. Snap snap snap. Hopefully it will all be over in one night. Then clean and re-check. Make breadbins available etc and covered rubbishbins and hope the guests use them.