HowUbe,
I think fungo did a great job of answering your question.
That is why it is important to discuss the possibilities before draft day. If a player gets a call on draft day and they say they will draft you for so and so amount, you should be prepared to answer yes or no. If yes is the answer, and one decides to sign and give up eligiblity, the advisor now becomes the agent (upon agreement)and he can negotiate things that are left out (school, extra money for that round, etc.). He cannot by NCAA regulations, talk to a team on the players behalf before that time, but it happens frequently. Rest assured if your son is expected to be the first in the next draft, deals are already being made. Likewise if a player signs with an agent before his signing, he has lost eligiblity for good. Important to make your player understand the implications of signing with an agent before negotiations, because if things don't work out, there is no school for the player. That is why it is important to trust the person you take on as an advisor.
I agree with FBM and Fungo, advisors and agents become a necessity at some point, and can be a vital link between player and club and help out in supplying necessary equipment, deals, that would otherwise cost the player.