An interesting body language 'tell' to watch for is what is called 'Eye Blocking Behaviour'. When
This behaviour is so hard wired into us that people born blind will cover their eyes when they hear things they don't like. This is a behaviour coming from our unconscious, driven by our limbic brain, so it is a good 'tell' to take note of. Know that if someone is agreeing to help you with something, but are engaging in this behaviour, that they are not very happy about doing it. Either respond to their discomfort by letting them off the hook or ensure that you reward and thank them appropriately for helping you out!