Details are not yet firm on this
The intention of it , is to allow a purchaser of a new Tesla to sell privately rather than trade in the car via Tesla. Tesla tends to under-price trade-ins (YMMV), and many can garner a higher price privately. It allows the private sale to go through Tesla a s a courtesy sale, therefore reducing the net sale price of the new Tesla by the value of the trade in. HST would only be paid on the net value.