Good points from both. I have recorded people who were insecure about their music and they wanted someone they respected to listen to it: it's almost always a disaster. I have had, several times, to gently tell a client that I was NOT working for the critic he/she brought in, but for the person right there in front of me. I have had people call me in a panic about a "problem" that some third party found in a mix. I usually wait a few days to cool off, frankly. There aren't many people whose taste (let alone, ears) I trust more than my own. Then there are the bass players who want the bass louder than everything else, and the guitar players who don't care how loud they are, as long as they are louder than the bass, and the drummers, who complain if you can hear anything but the drums. That said, there have been some really useful comments that I have gotten over the years, and I won't say it can't happen. Just be careful about the protocol. Don't say, "this really sucks: what does it need?" You are asking your friend to parade his or her knowledge as well as whatever he or she can make up on the spot. Instead, work to get your recording as good as you can, and then be open to comments.