To follow up, I bought one.
I went to Tesla Birmingham to show them the headlight photos and ask whether they would be repaired under warranty.
On the near side one, the answer was 100% yes.
On the off side one, the answer was maybe, we'd have to have a look. Which I think is fair enough.
Since Auto100 told me that they are making less than £100 on the car, they aren't interested in addressing any issues I might have. So I wasn't super comfortable buying from them.
While I was at Tesla, I invited them to show me the used inventory and the sales team persuaded me to buy a used one. Red 2018 75D.
Their approved used is £5k more expensive, but what swung it is that it has 3k fewer miles, MCU2 (upgraded), is guaranteed to be in perfect condition with new tyres and comes with a 10k miles/1 year Tesla warranty. It doesn't have the sub zero pack, though. But that's not really important to me.
The vehicle is being driven to Birmingham where I will inspect it prior to it having the CCS upgrade (which I'm having to pay another £200 for).
I was guaranteed by the head sales rep Sharon that they will fix any issues that I am not happy with.
So thank you for the advice.
Next I am researching about how to connect an SSD to my iPhone to watch any video recorded from the car.