Normally I would probably not be engaging here, but I take it seriously as a forum moderator that you've insinuated that something members of the forum have been doing for years pursuant to National's own policies is dishonest. So I'd like to take a moment to address your points.

I think your first class booking example a bit of an extreme analogy, don't you? We are not talking about that blogger who several years ago booked dozens of 1-hour car rentals in a day just to earn the 1000 bonus AA miles per rental or something.

In my mind, if you're doing something "sleazy" it's dishonest or immoral. So let's ask the question this way: If I booked a minivan that was more expensive to reserve when I made the booking, and when I arrived at the station and the aisle or executive selection only had minivans, would it be "sleazy" to ask the gate attendant to adjust the rate down to a midsize? Or what about if I booked a cheaper midsize only, and upon arrival at the station asked if I could take a minivan, and was told yes? Would that be "sleazy" even though the minivan may actually be significantly more expensive? Does the answer to either of those questions change, in your opinion, if I do or do not have actual knowledge of the different prices between the classes?

Perhaps a better analogy would be buying shoes online from a retailer like Zappo's. You know you're only going to keep one pair of brown shoes, but you order several pairs to try them on and see what you like. Some are cheaper, some are more expensive. Hopefully the cheaper pair does the trick, but maybe they won't fit right. Would it be "sleazy" by your definition to buy all 4 pairs of shoes, and then have Zappos eat the return shipping on 3 of them, even though you only wanted one pair all along? Of course not, because it's the company's policy to let you, the customer, order as many pairs of shoes as you want and they'll pay return shipping if you choose not to keep it. All of that is built into their business model and pricing.

I think the basic premise of your argument - that a reservation for a car is necessarily "withholding" it - is not sound. This isn't a zero sum calculation. When you have a large airport station with hundreds or thousands of cars available, your backup reservation has no bearing on price and no effect on general availability of cars. Similarly, the backup reservation is not having any effect on the company or on other renters. The pricing algorithms are not that advanced.

Now, if the backup reservation would have any meaningful effect - i.e., at a small non-Aisle station that's taking staff time to pre-print a contract, prep an extra car, or locate something they do not normally carry to fill your reservation, I think your argument may have some merit. But there'd be no point in doing a backup reservation at a non-aisle station because you're not going to be getting any chance of an aisle upgrade, unless for some reason the station is out of your booked class and they are forced to upgrade you.

A more interesting discussion is the overall "no-show" problem that plagues the rental car industry, which has nothing to do with a few Flyertalkers making a backup reservation from time to time. When I go to the rental car industry trade shows there is almost always a panel or other session dedicated to that topic. Some companies (not National) offer a discount to customers for paying up front and then making the rate non-refundable. Others enforce no-show fees. But how that's handled is up to the company to decide. Today, National's policy is to allow renters to make as many reservations as they want, cancel them at any time, or simply not show up at all. Tomorrow that could change.

I don't expect to change your mind and you're certainly welcome to your opinion. That's what makes the forum an interesting place!