Many of them will lie to get what they want, lie for a grade, or lie to avoid punishment. And they will do it without even thinking twice about it.
Of course I am not talking about every student when I make those comments, but it does describe many of them. If you think that students who lie are the rare exception then you are kidding yourself. If you think that only the lower level students are the ones who will lie then you are kidding yourself there, too.
So, be careful about trusting your students. Many of them are looking out for number one and will do whatever it takes to get ahead or save their skins. Don't believe everything you hear unless you really know the student well as a high character person. Check up on them.
You will be glad you did.