I've been a Select renter for the past 4 years or so and I have always been upgraded two to three car sizes. The best was a convertable for the price of an economy at MIA. The only time I had a slight problem was at TXL, I was taking the car into E. Europe and Avis doesn't allow VW, BMW, MB to be driven there. She did upgrade me to a Diesel instead after a kind word on how pretty she looked (and she did look pretty).