Suppose an `aalim were to visit your home (like you had him over for dinner or something). Someone, with say, abundant deeni knowledge (hafiz, fiqh, etc). Let's say it's time for maghrib. Of course, you would offer him to lead the prayer. But, would you push the issue if he legitimately refused? I'm guessing most of the time, if you are a sheikh, you wouldn't refuse if insisted, but sometimes out courtesy of the host, they do refuse. Which ruling takes precedence?