Absolutely they are. Dealerships have a wide range of options for making money; used car dealerships tend to be just that: they sell used cars. Of course they're all franchises or independently owned, so there is a lot of variance.

I will agree that they should definitely be doing an oil change on any car they're going to sell though. Buying the materials in bulk, they could be doing oil changes for $15 per car. Then they can add some "Full 30 point inspection!" to their sale pitch for changing the oil and wiggling a few things while they're under the car.