Perfume’s no good: smell at the back is rank (7)
I believe the answer is:
colonel
'is rank' is the definition.
(a military rank)
'perfume's no good smell at' is the wordplay.
'perfume' becomes 'cologne' (cologne is a kind of perfume).
'no' indicates named letters should be taken away.
'good' becomes 'g' (abbreviation).
'smell at' becomes 'l' (I can't justify this - if you can you should believe this answer much more).
'cologne' with 'g' taken out is 'colone'.
'colone'+'l'='COLONEL'
'the back' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
(Other definitions for colonel that I've seen before include "Commissioned officer" , "High-ranking officer" , "Senior army officer" , "Rank (below brigadier)" , "Commander" .)