I'll throw in my recent experience. When I bought my CPO P85, I asked about installing the 3rd row rear facing seats. The SvC ran the VIN, and told me it could be done, they would just need to order the parts and set up an appointment. The next available appointment was 6 weeks out. Ok, fine, I can wait, no big deal.
As time goes by, I started a short list of other things I wanted the SvC to check out. An alignment issue, LTE upgrade, seat belt that wouldn't retract. Nothing major, just little things. The appointment date came, I made sure they had a complete list of my concerns, and I was told it could all be done in a couple of days. Fortunately, we were given an S85 loaner with rear facing seats, so that was nice.
After the second day, we got a text that our Model S was next in line to be looked at. The third day, a text that said they were carefully diagnosing any and all problems. The fourth day we got a text that work had begun and we would be updated when our car was ready. Then we got a text that some parts were being overnighted for the rear facing seats and they were not sure when work would be completed.
I called the SvC just to check on when they thought the repairs would be completed, and to make sure everything had been diagnosed properly. The rep said they were only able to start on the rear facing seats when they realized they didn't have all the parts. The alignment had not been checked, and the LTE retrofit was in progress. The seat belts were a known issue but the parts were on back order and it would be at least 2 months before they could swap them out.
I told the rep it was no big deal, we were glad to have the S85 loaner and we could wait as long as it took to get everything done and done right. He seemed genuinely upset that it was not as smooth of a process as it could/should have been, and he promised they would get the car back to us as soon as possible.
We got the car back after a week, the alignment was fixed, the third row seats are in, and the LTE is set up and working. Now we just have to wait a couple of months for the seat belts to be repaired.
Overall, not a terrible experience, but certainly not the same experience I would have at my local Toyota dealership.