Originally Posted by jackal

Possibly, but in the vast majority of cases, it's the result of an automated computer program glitch. It's very rare to do this intentionally, since despite the claims of some people here, the vast majority of people are far happier being involuntarily upgraded to something larger than being involuntarily downgraded to something smaller. In other words, if someone books a fullsize and they're out, they'll complain less about being given a premium than if someone books a premium and is given a fullsize. Thus, it's far less problematic for a rental agency to overbook on smaller cars than larger cars, meaning it's not generally in their best interest to encourage people to book larger cars by pricing them lower.