Part of car seat salesperson lifted (6)
I believe the answer is:
bumper
'part of car' is the definition.
(I know that bumper part of motor car)
'seat salesperson lifted' is the wordplay.
'seat' becomes 'bum' (synonyms).
'salesperson' becomes 'rep' (sales rep).
'lifted' shows that the letters should be reversed in order (going up in down clue).
'rep' written backwards gives 'per'.
'bum'+'per'='BUMPER'
(Other definitions for bumper that I've seen before include "Glass filled to brim" , "jumbo" , "Something big" , "kind of car" , "Race for young horses" .)