Are you well qualified to give gear or talent advice to another class? We have all been there... It’s the typical “which is better?” discussion that happens in every group, raid or guild chat.
My guess is no, you are not well qualified. Many people aren’t even well qualified enough to give good advice on a talent spec they don’t play. But it doesn’t stop us from offering our advice, does it? If asked, most of us will provide some feedback to “help” the person make a decision. It certainly doesn’t stop us from offering our unsolicited opinion on drops. (“Ooh, that’s nice shammy gear!” -- Meanwhile the hunter in your group just died a little bit inside). And it certainly doesn’t stop people from posting nerf and overpowered threads on the forums.
I would hazard to guess that many people *think* they are well qualified because they have a high level alt of the class in question, or a great understanding of class mechanics, or play a “similar class”, or simply read forums and guides a lot, or all of the above. I would argue that while this person likely has a solid grasp of the class he wants to advise and what benefits the class, they still don’t have a great understanding of the class and offer poor mentorship, advice and opinions on gear and talent selection.
A friend of mine recently leveled a Druid up to 70 and in his 60’s moved from Balance to Feral. He knows my two main classes are Warrior and Rogue, so he sought my opinion on spec and talent selection given the similarity to Bear and Cat forms. While I certainly was helpful in this transition, it became obvious (to both of us), that while the advice was good, it wasn’t great. Primarily because there are lots of little Druid intricacies that I overlooked because I don’t play that class and spec in the end-game. In other words, my advice was better than nothing, but it didn’t provide him maximum benefit. In the end, it would have been far more helpful to simply point him out to some good Druid websites or the Elitist Jerks forums.