The scales don't lie.
→   거울은 거짓말을 안해요.

[예문]
A:I'm much lighter metric.There's been a mistake on my weight.
 키로그램으로 훨씬가벼워요.몸무게가 잘못됐어요.

B:The scales don't lie.
 거울은 거짓말을 안해요.

A:This isn't a vanity thing.
  괜히 그러는게 아니예요.

  -vanity :덧없음 ,무상함.