Most of the times demons have lied to me, it has been because I was not prepared to know the truth (they tell it to me later) or because the “lie” was the “truth” at that time, Sometimes they also joke in a macrocosmically sarcastic way, which could be mistaken as lying if you don’t have that sense of humour.
I would also like to add that my sucubbi and my incubus have a tendency to conspire in my favor behind my back, which involves lies that are much like if they were leading me to a surprise party, It is a way to keep their preparations unaltered, but sometimes I decide not to follow them for whatever reason.
Edit: Also, sometimes when unexperienced people or people that know nothing about their true will, ask for really stupid or self-harmful things, the demons will most likely tell them “yes, yes, of course I will give that to you” but nothing will happen. The reasons for them to do that are too many to be listed, but trust me, you will thank them later for doing that.