听其言而观其行

hear what he says and observe what he does (idiom, from Analects); judge a person not by his words, but by his actions

(idiom) you cannot always trust what you hear, but seeing is believing

to weigh up sb's words and observe their facial expression (idiom); to discern what sb thinks from his body language

to believe what one sees, not what one hears (idiom). Don't believe what people tell you until you see if for yourself.; It ain't necessarily so.

Explaining in words is not as good as teaching by example (idiom). Action speaks louder than words.

(idiom) to say one thing and do another