Hi HorseyMike,

Yes and no.
Definitions of what constitutes a fullsize, midsize, compact etc. do exist (based on internal space, wheelbase and other factors) but the rental companies are not obliged to follow those definitions, and likewise "or similar" is a vague term used everywhere. If you read the fine print it is impossible to deduct anything concrete out of it. When you reserve a car you are told what features it typically has but they make a point out of mentioning that the actual car you get may or may not have any particular feature.
They can call a Kia Rio a Luxury if they want and as a renter you cannot really do anything about it (although I'd love to hear about it ).

All rental companies (including the big and expensive ones) seem to be playing this game to some extent. Examples from other companies include Ford Focus being called a midsize, Pontiac G6 being called a standard.
And so on and so forth.

S.