modified
unprincipled, unethical, immoral, base, perfidious, degraded, selfish, self-seeking, petty, dishonest, knavish, wicked, tortuous, disingenuous, slippery, Machiavellian, casuistic, improper, Jesuitic*, perjured, recreant, rascally, pettifogging, shifty, underhanded, two-faced, double-faced, sly, conscienceless, arrant, venal, dishonorable, corrupt, roguish, illegitimate, illegal, unfair, unorthodox, questionable, unworthy, scandalous, disgraceful, degrading, shameless, shady*.
Antonyms honest*, scrupulous, fair-minded.