Paid posts are one of the best ways to monetize a blog; not just any blog but those with 2+ PR, good Alexa, reader community, social presence and MozRank.
What are Paid Posts?
Paid posts are basically sponsored posting where the advertiser expects any of the three things:
a full-review of their business product/s
a link back via author bio
a contextual link back
We bloggers charge for this sponsorship. Sometimes we have to write these paid posts to suit the requirement of the advertiser.