Cops' poker faces... or lack thereof

In general I like this series, but the cops don't have very good poker faces. All dramatic license, or are a lot of detectives this transparent?

Examples: Nancy seeing the pictures in Kevin's flat and fleeing with a look that gave away what she'd seen. The boss being so clumsy when pocketing Nancy's necklace, then announcing loudly in the office that she "found her necklace in the office." Nancy losing her *beep* on Shay when all she really needed to do was keep calm, tell him she had corroboration from the nursing home that he'd visited her mother, and let him sink himself with smugness.