Greek character in desperate bargaining set up (4)
I believe the answer is:
beta
'greek character' is the definition.
(letter from the Greek alphabet)
'in desperate bargaining set up' is the wordplay.
'in' indicates the answer is hidden within the clue.
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'ateb' can be found hidden inside 'desperate bargaining set'.
'ateb' in reverse letter order is 'BETA'.
(Other definitions for beta that I've seen before include "less than perfect mark" , "Greek letter -- second in order of importance" , "final test" , "testing stage" , "2nd letter of Greek alphabet" .)