Would make hardly any difference to me. As long as the person I was dealing with was honest and upfront and not a delboy car salesman trying to blag me.
Also, as long as the price was right, car was in the desired condition then I'd have no problem with it.
One thing to add, having more upmarket premises would perhaps inspire conficence in me that the compnay is prosperous and not out just to make a quick buck from a street corner type pitch. I would perhaps be more inclined to pay a little more for a car from a company that had smart premises. I would expect to pay less for a car from a smaller dealer with say, less cars and a lower standard of premises.