A Wash and Wax at the slip covers everything above the waterline you can reach from the dock and the deck: hull sides, topsides, non-skid, stainless, glass, isinglass, vinyl, and the cockpit. Wax or sealant goes on the hull sides and topsides by hand.
It does not include the bottom, which is diver work; the cabin, which is its own add-on; canvas or teak; or oxidation removal, which is a compound step done before wax on chalky gelcoat.
The reason boat work is priced by the foot is that a 40-footer has almost twice the surface of a 28-footer, and the time scales the same way. Flybridges, towers, and sportfish add surface and height on top of that.
Ask any detailer what is not included before you book. If they cannot tell you, the price will change on the dock.
Related: Wash and Wax, Cabin Interior. Or see boat washing and upkeep in Long Beach.