If you're arguing to put everything in a spreadsheet, or have us control the database and do without timestamping, I don't know what to say to you. Blockchain works here. Our business model isn't changing because you're saying we don't need it. Build a system like this yourself and we'll talk about it then.
Carfax is a vertically integrated service with very little of the complexity we're dealing with. And of course you can make do without blockchain. People made do without electricity and power tools. But here it's a cheap, faster, easier to use, and more trusted alternative. What's wrong with that?
Done. It's an email server. The person shipping the car takes a photograph of the odometer, emails it to the recipient, and then the recipient compares the photograph of the odometer with the car odometer. Any tampering which could be performed on the photo or its timestamp could be done equally to whatever log is entered into the blockchain, and the recipient knows that the photo must have been taken before the date when they received the email.
And if you use gmail, it's free.
Could someone tweak the image? Of course. But as a practical concern, probably less than 20 people have the image manipulation skill it would take to do something like this in the ~20 minute handoff period. The transporters certainly don't. This is a bullshit argument, and you know it. And these pictures are not just of the odometer, but the entire car, including the VIN. Photoshopping all of this believably would cost you more than just paying the damages on a joyride. It's a non-issue.
And I think you're misunderstanding something: the issue is not the time before the transporter get custody of the cars, but the many days that the cars are in transit cross-country. If the timestamp didn't exist at the time the transporter starts their journey, the next handoff knows something is up.
As for already trusting us, our clients do, yes, but the point of this solution is to increase the trust-level of custodianship handoff between people who are not our clients. A blockchain is a great solution for this, and a database is simply an inferior solution. And NO, they don't have to trust us to "push the right data on-chain". This logic runs in a very simple SPA and is immediately verifiable on-chain, without using our software, because the blockchain's global state is open.