The problem is that many agents aren't transparent, they're manipulative. They couch their advice as being in the best interest of the player and family. They frame their suggestions as being the best business practices. They sow seeds of doubt to keep kids or families from making decisions they think don't maximize their own commissions. They solicit offers/bids when they kids have stopped looking, to try and further drive up the price in the name of making sure the player/family get a "fair deal."That agent does not overrule anyone. He is the expert in negotiating a contract. He is telling them how to best maneuver the negotiations. The family has the decision to go wherever they want.
The premise behind many of their actions implies the schools are trying to screw the athletes and their families. It's pretty powerful to act skeptically concerned and just say, "are you sure you want to take xyz's offer, when abc told me the other day they would like to get you on campus and are considering an offer that's 50% higher than xyz?"
I'm sure there are some good ones that truly want the best deal (not the biggest deal) for their client. I know there are instances where they actually add value to a process. But there are lots of other instances where they only value they add is to their own pockets.