The agent/advisor and player relationship is personal. Sometimes the poor agent for one player is a great agent for another player. Usually those players considered among the best have several choices. There really are a lot of excellent agents.
That said, the truth is there are also a lot of bad apples in the bunch. Most all agents need to be good salesmen. Listen very carefully to what they are telling you. They all know the easiest thing in the world is to switch advisors. Sometimes you can tell if their advice is helping the player or protecting their own interest. Watch out for when your advisor is giving you bad advice
This is good advice, but how does a novice baseball parent know when the advice is bad? Since this is probably a first time deal for most, and the agent/advisor is probably a seasoned veteran, how do you know what advice is good and what advice is bad?
You are right, how does one know what advice is good and which is bad?
My suggestion would be to familiarize yourself with where your son may fall in the draft, if at all. Early projection means that your son will be getting lots of phone calls from lots of different type of advisors/agent. The way the draft is structured late pics do not really need an agent to help them to decide if they should go pro or to college, or stay in college or sign (seniors have no options really). A good advisor will make himself familiar with your son and his talent level, if he says he sees your son getting drafted early and PG or BA lists him as a late pick, well would you trust that advice?
As PG wrote these relationships are personal, it is up to that player (and his parents if HS age) to sort out what the advisor is advising without compromising his eligibility.
You can always ask questions here, and I know that Jerry Ford is always willing to give good advice! You can probably trust him more than anyone else!