The most common and most likely answer to this crossword clue is the 7 plus 2 letter word BELIEVE ME
I've seen this crossword clue in Financial Times
B
E
L
I
E
V
E
M
E
Buddy explains!
The straight part
We know that "Accept my word" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case accept my word = believe me.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.