The art and science of body language fascinates me but here's my disclaimer: I'm still a student. Taking that into account, here are a few things you might watch for in your next sales call.
When the person in front of you is looking to your right while talking they are trying to recall information. Remember, right is RIGHT. However, if they are moving their eyes to your left, they are accessing the storytelling part of the brain and may not be giving you the most accurate answer.
Arms and legs can tell you a lot. If the person's legs are crossed, they are putting up a barrier to you. They are concerned or threatened. You may want to change the subject.
If their arms and legs are not crossed and are in a normal position, they feel comfortable.
If they are standing or sitting with you, their feet will point in the area they are interested in. So if they are not pointing at you, cut the conversation short!
After becoming aware of the body language of others, try tuning in to your own to see what it reveals. You might be surprised.