Yes I can! Even before the TV show "Lie To Me" first started, I can tell if someone is lying. There are so many signs, physical, voice, eye movement, etc.
I think I can, especially if its one of my brothers or someone I know really well! I dont think Im easily convinced either, I always think through what people say before I believe them <3
The two most common signs that someone is lying are looking up and to the left and pupil dilation. That's from a scientific standpoint anyway, but you can easily train yourself not to look up, and with a lot of work your pupils won't dilate.
I can usually tell when someone is lying because of that and just because of other nervous mannerisms.