Even a fair condition Corvette deserves a little beauty parlor action before you attempt to sell it. You can improve your sales results measurably by simply making sure that you have cleaned out the old candy bar wrappers and mouse nests from the interior. You should at least wash and wax the outside and clean the wheels before you get ready for the sale.
Be sure to take a vacuum to the interior and try to get rid of any stale or musty smells. A discreet air freshener might not be a bad idea, but take it out before showing the car! You might consider taking the 'Vette to a detailing professional if it's a higher-value model.
At this point, it's also a good idea to take care of any low-cost deferred maintenance. Windshield wiper blades, burned out lights, leaking tires, and so on should all be fixed. If possible, make sure that everything works, from the stereo to the cruise control.
Note that any required certifications such as emissions testing or vehicle safety inspections are your responsibility to provide, and having them performed and ready will really set you apart from other sellers.
Finally, a fresh oil change and a full tank of gas have a good psychological effect on buyers.