Catch sight of opening for estate agent (4)
I believe the answer is:
espy
'catch sight of' is the definition.
(espying is a kind of catching sight of)
'opening for estate agent' is the wordplay.
'opening for' says to take the initial letters.
'agent' becomes 'spy' (spy is a kind of agent).
The first letter of 'estate' is 'e'.
'e'+'spy'='ESPY'
(Other definitions for espy that I've seen before include "Observe, notice" , "Catch sight of (poetic)" , "Discern" , "Detect" , "Spot; observe" .)