guileful

astute, facile, glib, sharp

crooked, deceitful, deceptive, dishonest, fraudulent, insinuating, knavish, Machiavellian, oblique, serpentine, shady, shifty, slippery, sneaky, treacherous, underhand, underhanded, unscrupulous

backhanded, double-dealing, hypocritical, insincere, left-handed, mealy, mealymouthed, smooth-tongued, two-faced

circuitous, circular, roundabout

clandestine, concealed, covert, furtive, hugger-mugger, secret, stealthy, surreptitious, undercover

calculating, plotting

unconscionable, unethical, unprincipled, unscrupulous

deceitful, deceiving, deluding, delusive, delusory, false

artful, beguiling, cagey (also cagy), crafty, cunning, foxy, slick, sly, subtle, wily

defrauding, devious, furtive, slippery, sneaking, sneaky, trickish, tricky

insidious, perfidious, treacherous