and carsidrect is for new cars, I think you are confusing them with cars.com
actually your point that they have a refund policy led me to go look at that page...and my opinion is now even worse. Apparently that money only gets you one car. So you can't cross shop the best deal on a Civic and a Corolla to see which is the best option, without paying even more money.
I happen to be at that specific point right now and if their service works as described on the many testimonials on the site and one on HN, I think paying $39 for it would be a great deal.
I do think you have a point in that, folks often come down to more than one choice on a model and make their final decision based on price. I think it would make sense for them to have a plan that supports this use case.
Carsdirect is a broker of used cars. They solve the problem of letting sellers find buyers and vice versa, not the same as making the process of buying a new car painless and shorter.
Most importantly though, their offer to refund your money for any reason makes this entire argument pointless. If they didn't think they could make you happier by saving you at least more than their fee, do you think they would make that promise?