The most common and most likely answer to this crossword clue is the 6 plus 1 plus 6 letter word RETURN A FAVOUR
I've seen this crossword clue in Financial Times
R
E
T
U
R
N
A
F
A
V
O
U
R
Buddy explains!
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.