Welcome to my world…
Received just now: “Hi, I wanted to check if you currently accept guest post or link placements on your website. If yes, could you please share your guidelines and pricing? Thanks.”
Response: “No, I don’t. Guest posts are by invitation only.”
Ethics Alarms 
My response would have been, “Have you read anything on the blog, up to and including the Comment Policies?”
Well, I have had that general thought for a number of brief visits by the soon-to-be-banned…
I heard this radio drama broadcast in 1977, and it’s stuck with me ever since.
Honestly though, it’s probably unethical not to provide a price for the invitation like $100,000 and guidelines that it has to comply with all ethics policies.
Just sayin…