I did have a confirmation email that listed the price and the car, the person behind the counter and the manager said they couldn't honor that deal because the car didn't exist and I had paid the rate for a lower tier of car. If I wanted a car that could fit 4 adults and luggage I had to pay the difference. It was Sixt in downtown Manhattan.

Searching for "Sixt bait and switch" returns a fair number of stories and reviews that are similar to my experience.