The most common and most likely answer to this crossword clue is the 8 letter word CONFOUND
I've seen this crossword clue in The Daily Telegraph
C
O
N
F
O
U
N
D
Buddy explains!

The straight part
We know that "Swindle" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case swindle = confound.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 CONFOUND mean?
CONFOUND noun- A confounding variable.
- To perplex or puzzle.
- To fail to see the difference; to mix up; to confuse right and wrong.
- To make something worse.
- To combine in a confused fashion; to mingle so as to make the parts indistinguishable.
- To cause to be ashamed; to abash.
- To defeat, to frustrate, to thwart.
- To damn (a mild oath).
- To bring to ruination.
- To stun, amaze