The most common and most likely answer to this crossword clue is the 4 plus 1 plus 5 letter word SOLD A DUMMY
I've seen this crossword clue in The Times
S
O
L
D
A
D
U
M
M
Y
Buddy explains!
The straight part
We know that "fooled" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fooled = sold a dummy.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.