The way I see it, only masters SHOULD be allowed to sell/promote skins on this site. If it's for the betterment of the community, then wouldn't a majority of the members understand?
That would be my personal preference and sentiment on the issue, as well. So if those were the rules (i.e. only Masters can do it) I don't think there would be a wide-spread problem of exploitation, seeing as how most of the Masters wouldn't take advantage of the community.
Then the only remaining issue would be, 'does the skin have to be uploaded to this site as well?' After thinking about it, I think it'd be safer to just say 'yes, it does'. Or, at least there should be plans to upload to WC if it isn't already. You can't always rely on common courtesy when you're thinking long-term; things change, people change.
I'm still ruminating over a hypothetical where the Master was in good-standing with the community and the site but just didn't upload here anymore (it's a stretch, I know, but I still think it should be considered or discussed). How would that Master go about informing his friends/people who might be interested, that are part of WC, without making a post here? Email all of them or just hope the word will spread?