Is it irreverent to question and check out messages that claim to come from God?

Not at all.  In fact it's just what God wants us to do.  About prophecy Paul says to the Thessalonians, "Test everything.  Hold on to the good."  God commended the Bereans who tested even the apostles' teaching by scripture before swallowing it.  Paul taught the Corinthians that while some were prophesying in church, others were to listen and judge what was coming out.  John wrote, "Dear friends, do not believe every spirit, but test the spirits to see whether they are from God, because many false prophets have gone out into the world."  It is easy to mistake our own thoughts or interpretations for a prompting from God.

Scripture gives a number of tests for detecting false prophecy.  A prophecy is false if

1.     an event is foretold but does not happen - Deuteronomy 18:21,22.

2.     the prophecy comes true but then the prophet counsels people to sin against God - Deuteronomy 13:1-3.

3.     the fruit of the prophet's life and his followers' lives is evil - Matthew 7:15-20.

4.     the prophet says Jesus is accursed (in contrast, no one can say "Jesus is Lord" except by the Holy Spirit) - 1 Corinthians 12:3.

5.     the prophet denies some fundamental of the Christian faith - 1 John 4:2,3.

6.     there is not a spirit of freedom but of coercion and manipulation - 2 Corinthians 3:17.