Uhm. I am not a lawyer of course. But should you not contact the site were the file was uploaded? Like with those dmca stuff?
Even if you retroactivly cancel the purchase - wich might be troublesome - this will not take the pirated copy off the net or off the users hard drive.
Also, you are talking about an asset not a game? You sure anyone would be interested in making games with pirated assets? Some gamers would play pirated games, of course. But devs using pirated assets? Why? If you try to release your game you would get serious problems and risk your game
And while I am at it, what kind of dev browsed illicit asset stores at all? Because, if the store the thing was uploaded to, is not illicit, just notify them and be done with it. They will remove it, since they are not illicit.