Smell in unpacked suitcase: cleaner appears (6)
I believe the answer is:
sponge
'suitcase cleaner appears' is the definition.
I can't judge whether this defines the answer.
'smell in unpacked' is the wordplay.
'smell' becomes 'pong' (pong can informally mean a bad smell).
'in' is an insertion indicator.
'unpacked' becomes 'se' (I can't justify this - if you can you should believe this answer much more).
'pong' placed within 'se' is 'SPONGE'.
(Other definitions for sponge that I've seen before include "Scrounge; wiper" , "Madeira, say" , "'Porous, absorbent substance (6)'" , "clean with damp cloth" , "Bathroom scrubber" .)