The most common and most likely answer to this crossword clue is the 7 letter word NAILERS
I've seen this crossword clue in The Guardian
N
A
I
L
E
R
S
Buddy explains!
The straight part
We know that "they expose lies" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case they expose lies = nailers.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does NAILERS mean?
NAILERS noun- One whose occupation is to make nails; a nail maker.
- One who fastens with, or drives, nails.
- A nailgun.
- A piece of dimensional lumber and/or plywood secured to the deck or wall which provides a receiving medium for the fasteners. (Sometimes referred to as blocking.)