Body language and facial expressions are not exact guides to detect when
someone is lying. However, they can guide you in a specific direction, to lead you to gather more information.
Another piece of the puzzle, you just need to figure out where to put it. The more you know a person, the easier it can be to tell their baseline, you just need to know what to look for.
For a little more information on interpreting whether a person might be deceptive, check out this article – https://www.forensicscolleges.com/blog/resources/10-signs-someone-is-lying
Keep in mind, a person might be displaying tension, at the same time might not be lying.
It’s all about understanding what you are seeing, then learning more.