paid guest blogging

Have you ever paid for guest blog posts on your own blog? If so, did you think it was worth it? How often do you do it? How much are you willing to pay?

I get requests from people who want to buy guest blogging on my blog. They want to pay me to let them blog, but their blogs are advertisement rich. I've never paid a blog to be a guest blogger. Have you ever done it? If so, was it successful for you all at?