You got to know how to hold 'em...
Seinfeld's “Alternate Side” episode (from the third season) has the perfect come back for those car rental agents that somehow don’t have the vehicles that were previously reserved by customers. This is a "copy/paste" from http://www.seinfeldscripts.com/TheAlternateSide.htm:
Rental car agent: Next please.
Elaine: Well, go, go.
Agent: Can I help you? Name please?
Jerry: Seinfeld. I made a reservation for a mid-size, and she's a small. I'm kidding around, of course.
Agent: I'm sorry, we have no mid-size available at the moment.
Jerry: I don't understand, I made a reservation, do you have my reservation?
Agent: Yes, we do, unfortunately we ran out of cars.
Jerry: But the reservation keeps the car here. That's why you have the reservation.
Agent: I know why we have reservations.
Jerry: I don't think you do. If you did, I'd have a car. See, you know how to take the reservation, you just don't know how to *hold* the reservation and that's really the most important part of the reservation, the holding. Anybody can just take them.
Agent: Let me, uh, speak with my supervisor.
(The agent goes into an office with a window in the door so she can be seen speaking with someone.)
Jerry: Uh, here we go. The supervisor. You know what she's saying over there?
Jerry: Hey Marge, you see those two people over there? They think I'm talking to you, so you pretend like you're talking to me, okay now you start talking.
Elaine: Oh, you mean like this? So it looks like I'm saying something but I'm not really saying anything at all?
Jerry: Now you say something else and they won't yell at me 'cause they thought I was checking with you.
Elaine: Okay, that's it. I think that's enough, see you later.
(The agent returns.)
Agent: I'm sorry, my supervisor says there's nothing we can do.
Jerry: Yeah, it looked as if you were in a real conversation over there.
Having the TV on as background “music” does help…