It isn't a huge ding and only lasts for about 2 years (and trails off in impact over that time period), but if you did so repeatedly, that would be a negative signal to future lenders.
https://www.experian.com/blogs/ask-experian/credit-education...
And what about the refund on your insurance, your DVLA registration, your time... etc. What an admin nightmare!
That said, my experience is with an all-cash/no-financing face-to-face purchase of a used car much cheaper than any Tesla, following a test drive and inspections both by the dealer and an independent inspector I chose, so mine was not all that similar of a situation.
Wow what if you've insured a $k car but use the policy to drive a $100k car and then total it?
They don't list what you actually bought. There's no way to know if you're underwater, and it doesn't matter because credit reports don't list your assets either.
You would need to do a lot of due diligence to make sure you really have no costs. Many car companies fully split their lending and you might end up with costs on not going through with lending even if you get your money back on the car.. Insurance companies, DMV registration taxes, etc, might try to hit you a little bit on rounding and can have some non-refundable charges but more significantly, will mess with you on paperwork which is all the hassle of work.
I doubt many people went through with that, though I can imagine people who started on impulse created weird situations for their sales teams and weren't worth the hassle.
All finance has a 14-day cooling off period so no worries there either.
Still, it's not hassle free: you have to arrange insurance, then cancel it, register the vehicle, unregister it, pay the VED, cancel that. It's definitely a PITA.
Yes not a failing to pay... but doesn't your credit report suddenly show £100k against your name? And they'll assume the car's deprecated so you'll be underwater. That's not as bad as failing to pay but I wouldn't want to be applying for a mortgage the next month.