Here are the offers I got from four places for my black 2019 Model 3 SR+, 30K miles
Tesla: $21,700 trade-in (would have also saved $1,600 in sales tax)
CarMax: $21,000
Driveway.com: $16,600
CarbuyerUSA: $27,800
Sold to the CarbuyerUSA and found the process easy. Getting Model Y later this week.