Every try to rent a truck for use as a truck? To haul rock for example? You will spend more than a day just finding a place that will allow that (everyone else will see the scratches and dents that does to the truck and charge you expensive damages). I've also called uhaul before and discovered they we sold out (uhaul doesn't allow rock type uses, but does cover some truck needs).

There are also times when you don't need a truck, just a larger car, renting that is $100/day. And again I've tried before and discovered the rental cars place was sold out when I needed one.