now what actually does happen if you prepaid but didnt show up?
You lose your money. There’s not a lot of ways to prepay a National rental domestically, but some do exist. They are commonly sold as vacation packages. Look at rental car options on Allegiant Air’s website for instance. It’s typically a poor idea to prepay, because you can almost always get a cheaper rate with postpay and coupons, you lose your ability to cancel or are charged a cancellation fee, (dependent on booking method) and many times, you won’t earn rental credit.