Reminds me of something a female friend told me about. She told me that someone, whenever they used to speak, would keep staring into her eyes and she'd feel like the guy was trying to manipulate her or something. =/ She'd have to look away since it was so uncomfortable.
Anyways, I work as a Sales Associate and customers constantly do the same thing to me as well. The way I understand it is that they're trying to intimidate or establish dominance over me. After assuming that, if I had the energy, I'd look at them right back in the eyes. ^__^ Either way, I'd keep eye contact as much as possible. I'd blink though as if I weren't trying to keep my focus on their eyes. Gotta make it look real right? Others would keep staring and not blink at all, which is really weird. =/
So if I know what you're talking about, I'd say that if they were giving you the manipulative stare, give it right back. XD But be BETTER at it than them. =) It's uncomfortable and will take some time and some work, but this will constantly be an issue for you if you don't fight back. Also understanding things makes it easier to find a solution for a problem. I understood this kind of behavior from customers to be them trying to intimidate me or establish dominance over me in order to push me into getting them discounts or giving free stuff. So I knew what I had to do from there. Not give in. =) And it's nice to see them confused or upset that they didn't get the desired response or reaction. XD
^__^ You're supposed to blink when you're looking back at the person. Otherwise it'd look like you were staring. By blinking, it makes it SEEM like you're not using that manipulative stare back on them.