One buying almost flawless jumper (9)
I believe the answer is:
purchaser
'one buying' is the definition.
'almost flawless jumper' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'flawless' becomes 'pure' (I've seen this before).
'jumper' becomes 'chaser' (both can refer to a horse).
'pure' with its final letter taken away is 'pur'.
'pur'+'chaser'='PURCHASER'
(Other definitions for purchaser that I've seen before include "he's bought" , "Punter" , "Buyer" , "I'll buy" , "One who buys something" .)