My recent experience was the same as Wigwam and Pops. We returned a VW for a BMW and the BMW dealer checked the car and we received an email from Motability before we had even driven off in the new car saying that the GCB was approved and the money arrived in our account a few days later.
As long as your car is tidy I wouldn’t worry. Some forum users have posted photos of cars with damage that is way more than ‘wear and tear’ and have still received their GCB, so the bar seems to be set quite low.