When you book through a prepaid third party site, the site has typically paid a heavily discounted rate for the room. The hotel has no access to anything you used to pay for the room, including a credit card. I have no idea what the hotel's experience has been, but if it suffers a high rate of vandalism or other damages, $300 isn't really that much. It's annoying, but it's one of the downsides of third party sites.