I don't speak legalese. Is there a list of each agency's cancellation policy in layman's terms? If not, can someone answer these questions?

Do you usually make more than one reservation for the same trip? For example, shop around, find multiple "good" rates, reserve 2 or 3, and wait to see which one goes up or down? When is it too late to cancel for a non-prepaid reservation?

What happens if I just don't show up for a non-prepaid reservation? Is there a penalty?

Here's why I'm asking. I can get an amazing rate and pick of the aisle with one agency. I need room for 6 people but there is no guarantee that the aisle will have a vehicle that suits my need. So, can I book another reservation at another agency for a large SUV or van in case I can't find what I need at the other agency?