sumnjiv

1. suspicious; dodgy
   Ispred zgrade stoji neki sumnjiv tip. — There's some suspicious guy standing outside the building.
   Policija je pronašla sumnjiv paket na stanici. — The police found a suspicious package at the station.
2. (of quality, value) doubtful; questionable
   Ta roba je sumnjivog kvaliteta. — Those goods are of questionable quality.

Sumnjiv means arousing suspicion; a distrustful person is sumnjičav.