You can eliminate a lot of wordy nonsense by just checking EBay "Sold Listings" for your particular car preference.Pay particular attention to those cars sold 'no reserve' .
The interesting aspect is how/why these few ,hard data points differ from Nada/Blue/Edmunds valuations. Data vs. guestimates vs endowment, take your pick.

If I was selling (ain't gonna happen this decade) I'd get the PPI myself. Done. Here sits the car, certified to be as well maintained as I said it was, in as great of shape as I claimed, and here's the price. Tank is full, oil just changed. Key is in my pocket. I'd even let the buyer start it cold if they wanted.

I found here in Ontario the supply is low, when i found my 99 with just over 30k miles, the asking price was 20k, we settled on 18. Plus a fair number of tools throw in. Here in Ontario when purchasing a used car, there is a government form that needs to be purchased which shows the book value of the car you are buying. Sales tax of 13% is paid on either the purchase price or book value, which ever is greater at the time of transfer. The book value on the government form was $4500. I was shocked that the value was so low. It does make me worry that if insurance ever becomes involved there will be a fight on my hands. As a result of the book value, I renegotiated the selling price for the car and bought likely the most expensive used floor jack ever for $13,500.

When my first Boxster was totalled while parked, I had a similar experience as Jake with my insurance company (other party at fault was vastly underinsured) where they determined the value of my car from comparable vehicles (similar to how its done in real estate). The NADA or Blue Book values never came into play.

I can only comment on what I see insurance companies value wrecked boxsters at. The price can vary by almost $10,000 on what they value a similar condition boxster at. I think it has to do a lot with the agent filling out the paperwork. The variations in price happens a lot more on base boxsters. I think the agent might be getting the values of an S boxster and a base confused. I've also noticed that location will affect the value sometimes. Generally speaking, values in California are the least and then followed by Florida, Colorado and Texas. It also seems like the poor states value them higher.

The supply in Ontario is not great! I was told that the price on the form was for the wholesale value of the car. I asked my agent about that, and was told that if totaled, the car would be valued at average replacement cost. My 2000 S with 62K was $6900 on the form. Desperate seller asking $15.5. Got him down to $12.5 after the PPI, and we split the cost of a control arm replacement and alignment for the safety inspection.

2 weeks ago I called my State Farm agent to inform them I was considering buying a CA salvage/rebuilt title 2015 Lexus GS-F, & ask how they would determine value if it was totaled. I was told State Farm will seek out similar vehicles for sale locally & base the value by averaging current prices. In my case when the vehicle has a salvage title they base value from the lowest priced comp's.

At one time, I was buying damaged cars and fixing them up to be driven. They all had California Salvage titles. I had an Audi S4, a Porsche 993 cab and BMW 530I. The kids had three VW Passats and an Audi A4. Two of the Passats, the Audi and BMW were all totaled in traffic accidents. State Farm treated all of the cars as if they had clean titles. They paid more on the cars than (IMHO) I could have ever sold them for.

And as a buyer I might suspect you choose a friendly mechanic and paid him to write you a good report. The whole point of a PPI is the buyer chooses the inspector and pays.

I've you even heard of bogus CPO reports of dealer inspections.