Note that for a courtesy car, Tesla insist on a £3000 excess or else add to your own insurance.
While I was waiting at my SC two weeks ago, one guy added a courtesy model S to his DL insurance at no additional premium but another had to pay DL £30 (both for one day, usual inconsistent insurance behaviour). A model X customer was trying out a courtesy Model 3 as a potential second car but the interior was filthy, full of litter, part eaten sandwiches & stank so he insisted Tesla valet it first. They did.
Another said he had used Tesla courtesy cars on several occasions - battered and filthy on handover but no checks when returning so he has no problem signing for the £3000 excess.
...I decided to take their offer of an Uber home & another back the next day even though they had a 2015 Model S if I wanted it.