And I believe that it has no effect on the price because the car rental companies have statistics for no shows so they overbook, just like airlines.
Again, I don't think anyone is disagreeing that they factor in a no-show percentage, in the past when fleet inventories were high, a 5% factor of no shows really didn't impact pricing as much as today.
Today fleet inventories are the lowest they have ever been (and probably should have been) which is resulting in prices being where they always should have been (sorry a minivan rental for $200 a week doesn't pay the bills), so a 5% no show factor really eats into the limited inventory, thus is why rates are jumping even higher then the already increased rates.
If you want to compare car rentals to airfare, thats a perfect way, then maybe you can see the impact of people buying airfare that don't show up has on inventory issues. Yes, every day people miss their flights (intentionally or unintentionally), cancel, etc, even if it means they lose money, however depending on the airfare they booked, they took away a lower cost seat from someone else. The good news is in most cases the person is penalized for this in the form of a change fee (or they booked a refundable airfare at a rate almost equal to a restricted first class ticket). Unfortunately car rental agencies haven't full implemented the fee for cancellation policy yet, although in some markets and on some fleets, this is starting to happen (which is a GREAT think IMO). So people book multiple reservations, taking up lower priced fare classes, resulting in others being unable to book lower rates, but people who do this seem to be out for themselves and no one else, shear lack of consumer responsibility.