People who work in prison may be cheats (6)
I believe the answer is:
screws
This clue is a double definition.
'people who work in prison' is the first definition.
(screw can mean a prison guard)
'be cheats' is the second definition.
(I've seen this before)
'may' is the link.
(Other definitions for screws that I've seen before include "increase the pressure" , "Fix in place (6)" , "Grooved fastening devices" , "Fastening devices and prison guards, colloquially" , "Put on" .)