Who in the world said anything about not trusting the coaches?
My goodness. If your son is good enough to play at State U., and he goes to their camp...they will recognize that he is good enough and begin talking to him about playing there. They, in fact, hope to do just that..."find" players they didn't know before or see more of players they did know about.
If, on the other hand, you overestimate your son's ability and send him to a camp for the sole purpose of being recruited by that school...and you took food off your table to do that...then you blew it, not the coach.
Consider that your general, "buyer beware." That is, if you wanna use camps for recruiting, point your energy and money to schools where your son, realistically, can play. Mom and Dad are often not too good at making that judgement...so don't blame the college coach. It is your choice on whether or not to write the check.