I offer sponsored posts on ErosBlog (written in-house, by me, in a suitable editorial voice) but I do not offer guest posts (written by who the fuck knows, in various plastic and commercial voices).
I explain this in my first email to potential sponsors, and again if it seems necessary.
Too often, someone who wants a guest post will just ignore my warnings and later demand "but we will prepare the post."
Today was one of those days. It never fails to leave a bad taste in my mouth.