The most common and most likely answer to this crossword clue is the 6 letter word TRY-ON
I've seen this crossword clue in Financial Times
T
R
Y
-
O
N
Buddy explains!
The straight part
We know that "Fitting/attempt to sneak an advantage" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fitting/attempt to sneak an advantage = try-on.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 TRY-ON mean?
TRY-ON noun- The act, or a session, of trying on clothing.