Mark down each damaged by a pound (7)
I believe the answer is:
cheapen
'mark down' is the definition.
(thesaurus)
'each damaged by a pound' is the wordplay.
'damaged' indicates an anagram.
'by' is a charade indicator (letters next to each other).
'a pound' becomes 'pen' (I've seen this before).
'each' is an anagram of 'chea'.
'chea'+'pen'='CHEAPEN'
(Other definitions for cheapen that I've seen before include "Demean - make less expensive" , "Debase" , "Reduce the price of" , "Decry or devalue" , "Cut" .)