a man can’t be known (/judged) by his looks; appearances are deceitful; never judge a person by (/from)appearance; you cannot judge a tree by its bark
❍ ～，别看他蔫头蔫脑的，打鬼子，做工作，样样都不让人，……(冯志《敌后武工队》266) Don’t be deceived by his appearance.When it comes to fighting the enemy or doing other work,he never gives away to anyone…
人不可貌相
you cannot judge a person by his appearance; you cannot judge a book by its cover
～，海水不可斗量a man cannot be judged by his appearance,nor can the sea be measured with a bushel
人不可貌相rén bù kě mào xiànɡ
指不能从人的外表来判断其好坏。比喻考察和评价一个人不能只看表面而轻易地下结论。don’t judge a man by his looks, Appearances are deceitful.