This is the way forwards, definitely - appearance should be irrelevant. Porsche lost out on selling my brother a 911 because he turned up in jeans and a t-shirt. They were rude and uninterested, so he showed them the cheque he was going to give them and went down the road to the TVR garage, where they gave him great service and sold him a very nice Chimaera, which he delighted in driving past the Porsche garage every day on his way to work

I tend to do the same, just dress casually and be polite. If they are interested in selling and not just being snobby then I am interested.