Priceline is quite clear about the fact that if you use the Name Your Own Price function to book a flight or hotel, then that's non-refundable. On the other hand, if you book a flight and then are offered an upsell car rental, it's not at all clear that booking is non-refundable.
Presumably somewhere in their massive terms and conditions, it's written in small letters. I've never heard of a non-refundable rental car reservation. The fact that they won't refund your money for that - and don't make it clear in advance that they're not going to refund your money - is unconscionable. There are a number of similar services on the market to Priceline.
While I've been a loyal Priceline customer for the last few years, this will be my last experience with them. And I'm going to take as many fellow Priceline customers with me as I can!