Check for following while buying:
The portion of the potato plant that is eaten is a part of the underground stem system used for food storage by the plant. "The potato tuber is an enlarged portion of the underground stem, rhizome or stolon. It represents mostly stored or surplus carbohydrate material not used by the plant for vegetative growth, fruiting and other essential life processes.
Potatoes of any kind or size should be firm, relatively smooth, clean, reasonably well shaped, not badly cut, bruised or skinned, nor should they show any green from light-burn. They should not be wilted or show sprouts. Cooking quality varies by variety and production areas.
You can make a delicious Potato fry.