Lying -
A lot of people can look you square in the eyes and lie. Add the fact that there are plenty of reasons why some people may avoid or seem to avoid eye contact, and eye contact just isn't an accurate indicator anymore.
The main indicators that someone is lying when they are answering a question are changes in their voice, speaking style, facial expressions, body positioning, and gestures.
Another great indicator for lies is moving an object between themselves and the person they are talking to. In an attempt to distance themselves without moving (because that would just be too obvious) they will usually put something between themselves and the person they are speaking to, as if they have liar written all over their face and this object will hide it from the person they are talking to. This could be done by simply moving something on a table, putting a coat between the two chairs you're sitting on, or even holding something in their hand, most commonly a cup, and slowly but constantly drinking it while you two are talking. This could also be a sign of boredom in the conversation, where if you think about it, subconsciously, that person wants to get away as well.
Something interesting here - constantly and slowly drinking something while talking is also a sign of interest/arousal (not always in the sexual way), but it is done differently. Keeping in mind the combination of all the other signs you're receiving as well, it's up to your better judgement which it really is.
And then there are tons of other factors you can look for like excessive anchoring, and such, but that's just going a bit further than we need to.