Nothing!
I reserved a minivan (Toyota Verso) through the Kayak website, and when I arrived at the pick-up location (Osaka Kansai Airport) they only had small cars available that weren’t suitable for my 6 person family. That would have forced us to rent two cars, which would have doubled the price. They blamed it on Kayak for false advertisement, because that location doesn’t even have minivans in their inventory. We chose to cancel both reservations (28 March and 02 April), and take a bus instead which was way cheaper than renting two small cars. Not sure I will ever make travel arrangements through Kayak again due to this fiasco.