The most common and most likely answer to this crossword clue is the 9 letter word ANACONDAS
I've seen this crossword clue in The Times
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More clues leading to the result ANACONDAS
Buddy explains!
The straight part
We know that "Cold-blooded customers" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case cold-blooded customers = anacondas.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 ANACONDAS mean?
ANACONDAS noun- Any of various large nonvenomous snakes of the genus Eunectes, found mainly in northern South America. Their length can grow to as much as 5 m (15 ft).
- (by extension) A large penis.