The easy answer
You are going to want to find someone with very little personal interest in the matter, or someone that has more to lose than gain by lying to you. In the former situation, it can be very difficult getting a qualified business professional to give you time of day if they are not getting anything from it themselves. However, it is not completely unheard of so you might as well give it a try. Once in a great while business leaders have been known to take an interest in certain individuals and to act as their mentors without any ulterior motives. Maybe they see a little bit themselves in these special cases, or maybe they just enjoy teaching those that they deem worthy of the lessons. Whatever the reason may be, you want to do whatever you can to find someone like this; someone that is willing to give you priceless advice simply because they find it emotionally satisfying. In other situations, you may have to rely on your own logic to try and determine the validity of the information shared with you. It can be difficult trying to prevent others from manipulating the situation by using their superior intellect or experience. You can always start by asking yourself if the person in question would be willing to risk tarnishing their reputation for the potential gain. Would their be any legal ramifications for their deceptive behavior? Unless dealing with a true psychopath that does not care about the consequences of their actions, you can rest assured that most people will avoid any situation that may cause them more pain than pleasure. If unable to gain anything using these previous two techniques, you can always resort to purchasing the advice that you seek. There are many great books and training programs that you can find on Amazon that can teach you about nearly any situation you may encounter in business. Although it comes at a price, this type of advice is at least acquired with just a one time fee and it is something that can be consulted repeatedly without risking bothering anyone.