WordNet sense 1 (not to be trusted):

slippery

WordNet sense 2 (not worthy of trust or belief):

untrusty

WordNet sense 3 (having concealed difficulty):

catchy

WordNet sense 4 (not easy; requiring great physical or mental effort to accomplish or comprehend or endure):

difficult, hard

WordNet sense 5 (marked by skill in deception):

crafty, cunning, guileful, knavish, slick, sly, wily, dodgy, tricksy

WordNet sense 6 (marked by skill in achieving a desired end especially with cunning or craft):

artful