The most common and most likely answer to this crossword clue is the 5 plus 3 letter word SHEEP DIP
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Buddy explains!
The straight part
We know that "Spooner (and farmer!) would say so" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case spooner (and farmer!) would say so = sheep dip.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 SHEEP DIP mean?
SHEEP DIP noun- A liquid formulation of insecticide and fungicide, used to protect sheep from infestation by external parasites.
- To replace someone's public service in the military and/or intelligence with another pretended occupation in order for them to serve as a covert intelligence agent.