You figure out if people are being genuine by listening to the way they talk. You need to also look at the person when talking to see if he or she is confident enough in what he is saying. Sometimes your guts help you know a misleading or genuine statement.
I've often asked myself this question. Then I realized it starts with me! I had to ask myself if I was being genuine or misleading to others? I believe you get back what you put into the Universe. Often times I was being what I thought everyone else was to me. Although a good person at heart, certain things would make me do and say things that ultimately made people question my character and if I was a liar or good person. Once I changed who I was deep inside and started being more honest with everyone, especially those who I love and loved me, I found that my suspicions of others went away. You have to start with the man in the mirror! I hope this helps you as much as it did for me, good luck! :)