Maybe they should install touch screen tablets at checkout and let the guest decide how much they would like to add to their bill. Maybe a slider scale, of course there wouldn't be a 0%, the slider scale would start at 5% and slide upwards to 25%. That way they make it as awkward and uncomfortable for the guest when they have to 'verbally' ask to have all discretionary fees removed from the bill. What a great parting encounter for the guest.