To me, it kind of depends on if the machine is clean or has an odor or not. If it was apparently taken care of and came out of a clean environment, I don't usually do much other than a quick wipe down. Any used bag gets replaced and filters washed, at the very least.
With my Eureka 1934A: threw away paper bag and old belt. Took entire machine apart down to motor. Washed all plastic parts in hot soapy water and scrubbed while wet to remove any scuffs. Turned bag inside out and put spring inside, zipped up and ran through washing machine. (Probably not the best idea but it worked just fine and no damage to the logo). Bag came out with no odor, hung outside to dry. Reassemble with new bag and belt, good to go.
Hoover Slimline: this had apparently been used without a bag it seemed, dust buildup inside with no bag. Scrubbed out entire unit inside and out to remove dust and minor rust. Disassembled exhaust/wiring chase to clean, scrubbed exhaust bellows to remove mildew. Cleaned floor tool and washed hose in bathtub. Polished paint with polishing compound and gave coat of wax. New bag and exhaust filter replaced with cut to fit electrostatic filter material.
Kenmore Progressive Direct Drive: this I admittedly brought into the house without cleaning up. It had a new bag in it and didn't appear to have anything nasty in it. I did give it a good wipe down, but I would like to go over it better to remove scuffs and the hose could use a good washing.
