If it were me, I'd look into the sites a bit further, such as the amount of traffic the sites are getting, how many members they have, would it be appropriate for my niche, etc.
If it is a brand new site just starting out and has very few members, I might make one marketing type post (assuming the site's rules allow it). I wouldn't spend a lot of time there, but I would keep an eye on my post and the future traffic it generates.
That's just my method.
Good luck and I hope that Wanelo and Fancy work out for you and produce some quality traffic and conversions.