The market is absolutely nuts right now. A friend of mine recently sold his M3 LR that he bought back in June at $48k to a small EV dealer here in my state for $53,500. That more than made up for sales tax he paid for it and the 20" black Tesla wheels he bought for it from a private seller. He decided he had the need for an SUV so he sold his M3, bought an ID.4, and didn't have to pay sales tax on it because his M3 was sold for more than the purchase price of the ID.4.
I am currently in the process of working with GiveMeTheVIN to finalize their purchase of my Mustang Mach-E Premium. I actually wasn't planning to sell it, but when they offered $54k for a car I paid $47k for in August, and for which I'll be receiving the full $7500 tax credit next spring, it changed my mind. I have had a M3 SR+ on order since early July, *almost* cancelled it when I bought the MME, but thank goodness I didn't! Now I'm just torn between hoping it gets delivered within 60 days of signing off on the bill of sale for the MME so I can get the sales tax break, or taking delivery in '22 when I *might* be able to get the renewed tax credit. Eh, it's a win win either way for me I suppose.
Incidentally, right before I decided to sell the MME, I requested a custom plate saying "REDSHFT," as that car is Rapid Red and it's a nod to other physics nerds. Wouldn't you know it, the SR+ I'm waiting for also happens to be red, so no need to scrap that plate!