How it is ensured that the replay shown for a particular incident is correct? For instance, while checking front foot no-ball, host broadcaster can edit and alter the footage to benefit the home team. Is match referee responsible for checking the correctness of the replays?
The host broadcaster is trusted with that responsiblity.
There have been instances of errors in replays, such as this case recently, but there's no evidence of cheating - it would involve collusion between teams, broadcasters and boards. Frankly, there's too much money involved for all of them to start that sort of messing.