Dark brown fur bishop found in auction (5)
I believe the answer is:
sable
'dark brown fur' is the definition.
(I've seen this in another clue)
'bishop found in auction' is the wordplay.
'bishop' becomes 'B' (chess abbreviation).
'found in' is an insertion indicator.
'auction' becomes 'sale' (I've seen this in other clues).
'b' put within 'sale' is 'SABLE'.
(Other definitions for sable that I've seen before include "Fur - heraldic black" , "Dark brown - black" , "Antelope, fur" , "Brush" , "Adventurous courage" .)