If a person has proper authorization to sell games that has one or more spriters-resource.com sprites would it be legal?
It depends on where that authorization comes from. We cannot license anything copyrighted but if you somehow had consent from all copyright holders to use their property in a commercial game, then sure.
Good question!
It's worthy to note that simply using the assets in the gallery as references (i.e visual guide) for your own original work, that's ok as well and you don't need to worry about legal issues.
No, nothing you find here can be used in any commercial application for any reason.