straight from the horse's mouth

straight from the horse's mouth (from a reliable source) — из первых рук, из/от первоисточника; из надежных источников; из достоверного источника

Example: get the news/ find out about sth straight from the horse's mouth — узнать ч-л из надёжного источника/из первых рук/из первоисточника

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This has to do with looking at teeth to establish age and therefore value; this information is likely to be more accurate than any other, such as that provided by a dishonest horse-trader.

Opp.
[get the wind of sth]