Green’s Dictionary of Slang

dubious, suspicious.

1904		Sydney Sportsman (Surry Hills, NSW) 30 Mar. 4/1: The surroundings of cycle racing grow ‘smellier’ with each succeeding day.
1923		J. Manchon Le Slang.
1933		B. Ross Tragedy of Z 56: So that’s the kind of smelly spalpeen this gorilla was!
1948		D. Dodge Bullets For The Bridegroom (1953) 31: Something was very smelly somewhere.
1965		R.L. Pike Mute Witness (1997) 7: Unless there’s been a pretty smelly deal made ...
1970		G.F. Newman Sir, You Bastard 202: Seems a bit smelly, Terry.
2012		(con. 1943) G.S. Manson Coorparoo Blues [ebook] ‘Stay away from this one [i.e. an investigation]. It’s smelly’.