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Why not try selling it to a dealer or CarMax? I sold my 2014 Model S to a BMW dealer. They gave me more than trade-in book value for it. And yes, I sold it outright to them (not a trade).
I went to their online appraiser and it offered me $49K which was around the standard trade-in value. I went to the dealer and had them manually appraise the car. I told them I was going to shop-around for offers and the highest offer wins the car. I had their online offer in my pocket. I didn't even shop anywhere else because they offered me $51K and I was more than happy with that. It was a base S60 with pano as the only option. It was over 2 years old and had over 30K miles on it.
In fairness, this dealer is part of a large auto group and they told me there was an employee at one of the other dealerships looking for a Tesla so they probably offered me more than trade because they weren't reselling it. I got lucky I suppose.
I got a great price for my Model S from Vroom. I don't remember the specifics, but it was thousands higher than Carmax, Tesla or Roadster. Worth checking out some of those online car buying services as their prices can vary a lot but good sales prices can be found.