I successfully bid a rental car on National with an all in price on priceline for my elderly parents. When they showed up to get the car, the National people provided a more expensive car.
When the car was returned National charged an additional $423 for the upgrade alleging that it was requested when it was not and basically subverted the entire goal of the priceline bidding process. I think that Priceline needs to gets is vendors in line and should demand that National refund the charge which was not authorized and was contrary to the whole process. I think that this is an unfair and deceptive business act by National and Priceline and I intend to write to them and copy FTC and Conde Nast and one else who will listen to me.
Interestingly this also happened with Avis but Avis only charged the airport fees which are also supposed to be included. If the vendors will not honor the contracts that are bid then there is no sense using priceline because the consumer has all the risk and none of the reward if the consumer is just going to be charged the full price.