We have had a lot of private sales posted here recently and they often turn out to be items listed for sale on Ebay, Bonanza, Etsy, Bagnatic, DeluxeMall, Siam Brand Name and other selling venues, including blogs.
We ask for the information in the first post to help people here determine authenticity. If people don't want to give that information, that's fine. But it really makes us disinclined to answer private sale requests. And it often makes it impossible to help.
If posters don't want to provide the information we request, no problem. I suggest using a paid service. There are several excellent ones and you won't have to disclose the selling venue here.