Understanding landlord's profit? (7)
I believe the answer is:
bargain
'understanding' is the definition.
(bargain is a kind of understanding)
'landlord's profit?' is the wordplay.
'landlord's' becomes 'bar' (I am not sure about this - if you are sure you should believe this answer much more).
'profit?' becomes 'gain' ('gain' can be a synonym of 'profit').
'bar'+'gain'='BARGAIN'
(Other definitions for bargain that I've seen before include "Favourable transaction" , "Cheap acquisition" , "Agreement, snip" , "understanding" , "Great deal!" .)