As we progress through life, we start to encounter people that know more than we do, less than we do, and just as much as we do in certain realms. In the firearms industry, we see a great deal of people that fall into both categories, but also we have the people that appear to know nothing that are wizards of their craft, and the people that want to appear to be an expert that lacks basic knowledge.
To compound this further, some of the actual experts may disagree on certain things based specifically on their (very valid) experiences. So now we have a legitimate expert teaching contradictory things based on an experience the other expert has not had. Neither person is qrong, they just don't see the whole picture.
In my opinion, you need to be able to use the a criteria for what information is good. Mine is as follows:
1) Does it pass the logic test? Does it stand up to critical thinking?
2) Has it been tested? Has this theory or method been used in the world?
3) Is it repeatable? Did it only work the one time in that particular circumstance or can it be assumed that it will work in other situations?
4) Is it usable? Is the information usable to me?
If you find someone that can give you all these things or you can verify them yourself, you have met someone with expertise in that area. Gather all the pertinent information that you can from them and add it to your knowledge.
Plain and simple, all information is not created equal. Everyone's opinion is not equally valuable. Experience, knowledge and skill level factor into how valuable the information can be to the end user.
Everyone is a genius at something, whether it's building rockets or playing with Legos. Make sure that your expert is an expert in the field you are asking about.