One who exploits us with a half of beer (4)
I believe the answer is:
user
'one who exploits' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'us with a half of beer' is the wordplay.
'with' means one lot of letters go next to another.
'a half of' means to take half the letters.
'beer' halved is 'er'.
'us'+'er'='USER'
Can you help me to learn more?
(Other definitions for user that I've seen before include "Manipulator" , "One taking drugs" , "Ruse for employer" , "One who works an appliance" , "Druggie" .)