As long as the place was clean and it looked like you cared about the place, I wouldn't care if it was an old petrol station. Cleanliness and quality of the cars would be what swayed me. It does start coming into it more when you are spending more than, say, £25k on a car. But if the place is smart, freshly painted, and organised, it gives the impression of a well run business.
Some of the poshest looking restaurants I've eaten in have served the worst food!