Beware of wolves in sheep's clothing

मुखं पद्मदलाकारम्
वाचा चन्दनशीतला ।
हृदयं क्रोधसंयुक्तम्
त्रिविधं धूर्तलक्षणम् ॥

A lovely face as beautiful as a lotus petal, pleasing words as attractive as the fragrances of sandalwood, a furious heart filled with violent rage; these are the three characteristic qualities of cunning people.

All that glitters is not gold.
Appearances can be deceptive.
Beware of wolves in sheep's clothing.