I don't have any answer to your specific questions, just a thought on terminology:
While usage may vary, at least from the Internet Marketing and blogging worlds where I live, there's a clear distinction between a "guest post"
and a "sponsored post"
free, and you'd accept such posts for the value the content (or the expert) will bring to your website and audience. In some cases, you (the site owner) may even pursue a recognized industry expert to make a guest post for you.Sponsored posts
(aka paid post, pay per post, paid endorsements, etc), on the other hand, are typically paid for. The ethics police
prefers you clearly and always disclose sponsored posts as such. In some countries, this may actually be required. And Google suggests (requires?) you mark any links in paid or sponsored posts with a "nofollow" link attribute (see https://support.google.com/webmasters/a ... 6356?hl=en