The most common and most likely answer to this crossword clue is the 9 letter word MUCK-RAKE
I've seen this crossword clue in Financial Times
M
U
C
K
-
R
A
K
E
Buddy explains!
The straight part
We know that "Dig for dirt" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dig for dirt = muck-rake.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.