To keep a carved pumpkin looking perfectly pristine for a few days, hairspray or a bleach solution might work.
But to keep one looking okay for as long as possible, it came down to a tie between a pricey commercial spray, and...nothing.
It seems just carving the pumpkin, and letting the cut surfaces heal and dry out a little, is the best strategy, of the ones they tried.
Interesting that they didn't try smoking them...
"the qualities of these bacteria, like the heat of the sun, electricity, or the qualities of metals, are part of the storehouse of knowledge of all men. They are manifestations of the laws of nature, free to all men and reserved exclusively to none." SCOTUS, Funk Bros. Seed Co. v. Kale Inoculant Co.