In the Dealerships/Showroom, the "Gallery View" option is ghosted (unavailable) for the "standard" cars, while the "premium" ones will have this option available. I think this is a pretty fool-proof way of detection.
A little harder perhaps, but you can also spot the difference in the Dealerships pages, by recognizing the less transparent greenish tinted window glass of the "standard" cars. On the "premium" cars you can see the modeled interior through the glass.