No, since Feb. 2013 you can not post to other people’s walls any more via API (you can only use the feed dialog and have the user trigger the post client-side themselves).
And IMHO what you are trying to do is exactly the reason for this change – posting “adverts” to other people’s walls is what I would consider to be pure spam. (And if FB’s Platform Policies allow your “business model” at all is questionable as well, I think.)