Same word as dirty-dealing:

clandestine,concealed,crafty,crooked,cunning,deceptive,devious,dirty-dealing,dishonest, dishonorable, double-crossing,duplicitous,fraudulent,furtive, guileful, hush-hush,indirect,insidious,oblique, on the QT, on the quiet,secret,secretive,shady, shifty,sl