Polish expert (4)
I believe the answer is:
buff
This clue is a double definition.
'polish' is the first definition.
(buffing is a kind of polishing)
'expert?' is the second definition.
(buff can mean an expert or aficionado)
(Other definitions for buff that I've seen before include "fan of > nudism?" , "light shade" , "Polish - fan" , "with attractively well-developed muscles" , "Informal enthusiast - polish him" .)