One owing money returning bed to seller in the end (6)
I believe the answer is:
debtor
'one owing money' is the definition.
(I've seen this before)
'returning bed to seller in the end' is the wordplay.
'returning' says the letters should be written in reverse.
'in the end' says to take the final letters.
The final letter of 'seller' is 'r'.
'bed' backwards is 'deb'.
'deb'+'to'+'r'='DEBTOR'
(Other definitions for debtor that I've seen before include "One who owes money" , "One owing money" , "Person who owes money" , "Someone owing money" , "Borrower" .)