This day, NO cars. Reservation was for noon. I waited until 1. Was told no cars until 4 pm. My appt was at 2:30. This was a neighborhood location, so nothing Hertz related nearby. Finally made an online reservation with Enterprise. I will give the Hertz guy credit for transporting me to Enterprise.
The most similar thing that has happened to me in my years of traveling was arriving at a Sheraton Hotel in Houston, somewhere along the Katy Freeway, at 1:00 am (with an 8:00 am meeting the next morning), and was turned away because they didn't have any rooms. What was even more galling was that I had called about noon to advise them that i was going to be arriving late, and they said no problem. (And, yes, the reservation was a late arrival secured with a credit card.). They instead directed me to a La Quinta Inn about ten miles closer to downtown.
And I had to pay for the room at the La Quinta. They didn't charge my credit card, but I'm sure that if I hadn't showed up they would have charged me for the room. When I complained to Sheraton afterward they apologized, but offered no compensation, and complained about how unfortunate it was that they had to send a customer to one of their competitors.
FWIW - the night desk clerk (and, as we all know, the night desk positions are so coveted that only the elite and most knowledgeable staffers fill those slots and

). Said that a group of people at the hotel that were scheduled had refused to check out, and that under Texas law the hotel couldn't evict them.
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Returning to rental cars, there was a time a few years back when I had a reservation at my neighborhood Hertz location. It's one of those places in the lobby of a hotel, where they have at most two people around, and often only one person. So that staff does all of the work, including getting cars washed, and filling gas tanks. Also, they sometimes get involved with ferrying cars between locations to meet reservations.
I rent from that shop regularly; I'm on a first name basis with the crew, and they've given me outstanding service over the years. And they are usually very good about scheduling their errands so that there is someone around or in the vicinity when there is a scheduled pickup.
This time I arrived and there was no one there. When I called the number provided for times when the office wasn't staffed (goes to the cell phone for whomever is on duty), there was no answer, I waited half an hour, calling the contact number periodically without answer.
I had an appointment to get to, so finally I gave up and walked across the parking lot to the Avis counter at a hotel next door, and did a walk-in rental at that location. Apparently I was the second or third person that morning to have had that problem.