Many times we are in situations where we know very few players in a game that we are playing with. We also will be in pots where we have no idea what the other players will do. When this happens we can fall back on little tidbits of information from stereotyping our opponents.
If you have a player that looks like Grandma Ethel who is 90 and needs a walker she probably will not bluff you often. If she is going to the river with you and she raises you, unless you have the nuts, I would fold. She will have what you think she has and that is the best hand.
If Jimmy is a 20 year old aspiring poker player with his sweet girl friend on the rail blowing him kisses and he raises you on the river when the flush or straight is blown on the river he is probably bluffing. Take a look at the people that you are playing with and see what you see. Many things that you see can and will tip you off about one’s play.
Whether a person is a male, a female, well-dressed, poorly dressed slob, reading a sports ticker, wearing headphones, overweight, anorexic, wearing lots of jewelry, not wearing a wedding ring, drinking booze, silent, boisterous, friendly, obnoxious, calm etc. you should take notice. When you have nothing else to go on you need to rely on you instinct and your first impression.