People aren't going to like my response but whatever, i'm only being real. There is NO way to resolve this issue, you just need to suck it up and move on. YES they are stealing your work, YES you worked hard to earn that money, but that's the way the internet goes, the quicker you realize this and accept it the easier it will be. I'm not saying what they are doing is right, but honest people will still purchase your skins, and if your skin is not selling as much as you thought it might, then pirates are not to blame for that. This is one of many sites that will come and go, if you manage to somehow by the grace of god shut this site down, another will pop up in it's place, as i said, that's how the internet works. Do not take this the wrong way, but skinners are the small fish in the world of pirating, you should be lucky that you only found one small site that not a whole lot of people visit, rather than software venders who have their software pirated all over the place. This doesn't mean you don't work as hard to make your product, it just means that you "technically" speaking, aren't as important to pirates as big named software.
With that said, the topic of somehow encrypting the skins comes up, and in my opinion there is no way to do this whilst keeping everyone happy. So you encrypt the skins, does that mean that you couldn't open them in skin studio any longer? If that's the case then you are probably looking at more backlash for that then pirating itself, because while there are many skins that i like to use, some elements of the skin i like to edit myself because I dislike it or it's bugged etc.. the list goes on. But taking away the ability to edit something as i see fit, without the intent to distribute would cause major concern for windowblinds purchasers.
I'm not trying to be an ass, and rain on everyone's "i hate piracy" parade, but i'm sure skinners like vstyler and essorant etc make a nice profit from skins at wincustomize, enough so that they keep pumping out quality skins every other week. If you feel that your skin is suffering in sales because of pirating than you are dilusional, and need to place blame on something other than pirates because the honest to god truth is that people that download pirated skins, were NEVER going to purchase them to begin with, that's how leechers work. It's understandable to be upset, but its not going to change anything, this is just how things work.