You can't judge a book by its cover

bʌfɔː jeɪəfɔː jɪθɹiː maʊfɔː kwθɹiː ɹɛntuː bʌfɔː jafɔːɹəʊ jɪθɹiː mafɔːɹəʊ kwθɹiː ɹɛtuːn

In Chinese 不要以貌取人 (bù yào yǐ mào qǔ rén)

This proverb is commonly used in Chinese culture to advise against judging based on appearances.