Like all vehicles, you gotta shop around if you want the best offer.
Lowest offer usually comes from Tesla. It is also the most convenient. You simply drive your car to the delivery center, and drive home in the new one. Don't even need to wash the car.
Next best offers will come from wholesalers like competitive dealerships, Carvana, Car Max or the on line buyer, Current Automotive.
They give you a price, and you drop off your car within the time window and walk away with a check. Need to bring a friend to drive you home or Uber/Lyft
Best $ will usually come from selling it yourself retail. Offer it up on line, or park it on the street with a sign. Buyers will come, and be prepared to answer a ton of questions, send a ton of pictures, and get lots of low ball offers. They tend to pick apart your car, look for any possible flaw or missing option. When you get an offer you will accept, you will need to send the buyer all the details, wait for him to get financing or arrange the money. You will need to work out a way to have them send you the money, send them the title and arrange delivery or pickup. This is obviously the most difficult and time consuming, but can be very financially rewarding.
I ended up using Currentautomotive.com. They gave me an easy sale. I sent them pictures and they sent me a higher offer than the other options. I sent them my title and they wired me the money. Once the money was in the account they have arranged to have a driver pick up my car. They are former Tesla people, appreciate the cars and know what they can offer.