The most common and most likely answer to this crossword clue is the 6 letter word CAYMAN
I've seen this crossword clue in The Guardian
C
A
Y
M
A
N
More clues leading to the result CAYMAN
Buddy explains!

The straight part
We know that "Dealer" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dealer = cayman.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 CAYMAN mean?
CAYMAN noun- Any of the relatively small crocodilians of genus Caiman, within family Alligatoridae.
- A semi-aquatic lizard, of the genus Dracaena, found in South America. To differentiate from caimans, they are referred to as caiman lizards.