I never trust someone who can't look me in the eye while talking to me. I'm not staring them down or hoping for them to do so, it's a sign of respect and open honesty.
I was always taught to look people in the eye when speaking to them because it the respectful thing to do! When someone doesn't look me in the eye when talking to me I wonder what they are hiding!
In many cultures looking directly at someone, you know, like eye contact...is actually considered rude!... and for those individuals that are shy or have had more than their fair share of scolding or lectures...they too, may not look at you the whole time, but it doesn't always mean they are being rude...they're just listening carefully to what you are saying... Some people are rude, also...not necessarily though...
I work with a shy woman and when I go to her office to ask her a question she stares right at my crotch while she is talking to me...it is very un-nerving. I think I might walk in there one day with my fly down and see what she has to say to that.
Yes, makes you wonder what they are hiding
Some are just shy