The eyes tell a lot about you, yes. But it's important to see body language and eye contact together, do not focus on just eye movement. Or just body langyage. They work together to give you clues on what's going on.
A person, when lying, will often avoid eye contact. But seeing someone avoid eye contact is not enough to say that the person is lying. After all, he may just be shy, or tired.
But if you look at body language and eye contact together, you would see extra signals, like forced smiles and exaggerated hand gestures. As liars usually have to think hard about what to say next, they speak looking distracted and speech may sound hesitant. Shifting the weight from one foot to another more often than you would consider normal is also a sign.
Don't get too trusting when someone is looking straight at you! Many accomplished liars realize that their eye movement may give them away, and will look straight at you thinking that no eye movement will keep them safe. Unfortunately, no eye movement is also unnatural, so this may give them away as well.
Aah... the 'Gaze'. Making prolonged eye contact is one of the first things that comes to mind when the subject goes to flirting. And we have to say, when someone is looking over to you, staring at you, not breaking eye contact when your eyes interlock... well, it's likely they have an interest in you.
But imagine that there was only the stare. Nothing else in the body language that would indicate a romantic interest. No smile. No hand or body movement. Wouldn't that be creepy? I think so.
It's another example of how body language and eye contact should work together. Make eye contact and smile. But there's more you can do...
Men are known pump up certain muscles to make them appear bigger. If they see someone interesting,, they can hold a tightened flex forever! Women are famous for sucking in their belly gut to make it look smaller, and stick out the chest to make their breasts look larger.
In the end, though, flirting does always start with making eye contact!