It wouldn't surprise me if they reach out to the commercial sites that act as intermediaries and let them know that they can and will cancel any reservations they feel are a violation of DVC membership agreement. DVC would only have to cancel a few to have a massive impact on the commercial sites business model. Word would spread quickly that people traveled to WDW to find out they had no reservation. Sure, they will get reimbursed (may be get one of those coveted vouchers) but those points may now be useless to the owner with it being too late to bank or go into holding.Maybe, but I'm inclined to believe that they will still look for patterns / volume and a few rentals using the internet to advertise won't be an issue. If that isn't true, IMO, we will hear about it very soon.