In the past you could change a prepaid to a different date/location at whatever current prices are. But that new reservation needs to cost as much or more as your prepay, otherwise you will "lose the difference."

I've started to avoid prepaying with Avis because if I arrive at a station and see a very long line, or a lack of vehicles, I am booking at a different company on the spot (and paying way more). Just too many fails with Avis in the past couple years. When things go as they are intended to go, Avis is still great. But if not, the waste of time is more than I am willing to accept. And yes I am PC- it doesn't matter. Same inconsistency.