From Doug in Alabama:
A well-known grandmaster told me to never read a chess book by a non-GM. He also recommended anything by John Nunn. Is this true?

Silman replies:
This reminds me of a German baker who told me to “Never buy fresh baked goods from anyone but German bakers!” Yeah, sure – no conflict of interests there! As the old saying goes, “Never say never.”

Reading books that are only by grandmasters is a joke. The same can be said about only looking at games by grandmasters. A game by a 1600 player can be far more instructive (for lower rated players) than a game by Kasparov if a teacher/writer uses it to show you the kinds of errors you yourself make. This lets you identify with what's going on, thus making things more personal. Of course, I'm not saying that grandmaster games shouldn't be studied. They should, and the more the better. But there's a place for other games too, depending on what you're hoping to get out of them.

Some GMs can teach well, some can't. Some can write well, some can't. Some can communicate ideas in a clear and enjoyable manner. Some can't.

Books by IMs can also be very interesting or very instructive, IF they have writing and teaching talent. But, in general, I rarely (note I didn’t say “never”) recommend chess books by anyone under that because they usually don't know what in the hell they are talking about (an author must have the chess strength to assess a position in a competent way). I should also add that owning Fritz doesn’t mean you know what’s going on, or that you can share this knowledge with students that look to you for guidance.

I can just imagine the dialogue:
Student: “So what’s going on here?”
1800 Teacher: “White is up by 0.34!”
Student: “I don’t know what that means. Besides, why is he up 0.34?”
1800 Teacher: “If you can’t see 0.34 when it’s staring you in the face, then there’s nothing that can be done! You’re hopeless!”

HOWEVER, a 1600 player teaching a class of beginners can often be a far better teacher than any titled player. Again, teaching is a talent unto itself, and the teacher's actual strength doesn't matter much if his pupils are just starting out.

Finally, there is absolutely no doubt that Nunn is a great chess writer. But his stuff tends to be more advanced (minimum 1800 right up to titled levels). I wouldn't recommend most of his books for players too far under that rating.