In the hotel business, we had two types of reservations - non-guaranteed and guaranteed.
- Non-guaranteed were referred to as 4pm reservations, because the guest had to arrive prior to 4pm, or forfeit the room (no deposit or credit card was needed to make the reservation.) Guests were still encouraged to cancel if plans changed, but weren't out anything if they didn't. The beauty is, the room was available to sell after 4pm, so we could accomodate travelers desperate to find a room during the busy season.
- Guaranteed reservations held a room all night. No shows were charged the first night's room & tax. However, if the reservation was canceled by 4pm, on the day of arrival, no fees were assessed.
I know it would be difficult to use this same system at campgrounds, but it would reduce the number of vacant sites during the busy season.