If you have a wireless go out to where he stands at sound check and let him dial you in and then decide if you like the way he hears you...
In a perfect world/room flat would be the rule but reality isn't perfect and a good sound man can save you from an imperfect room...
Some sound men just have issues with being the guy in charge, they don't like to be challenged.
And on that note, for a bit of fun on the topic Aynsley Lister
Sound Man