It is common to hear of higher percentages (10% or more) for agents involving Latin American players.
6% for an American player is astronomical. We have lots of experience in this area (though we are not in that business) I feel pretty secure in saying the majority charge 4% of the entire amount of the signing bonus. 4% is the most common percentage.
Again, there are exceptions! Usually the exceptions would be less than 4%. Afterall, it's a competitive business, As TxMom and many others on this board can tell you. Some have been successful negotiating a lower % with the advisor. It's been our experience that most of the top agents will not negotiate their fees.
We have seen examples of advisors who are trying to sell their services despite never having seen the player play. To us this is a no no. Always ask where and when they have seen your player. Ask what they saw.
We once received a call from an agent who was trying to get our blessing for him to advise one of our players. I asked how many times he has seen him play? He said "only once, but it was enough". I asked where he saw him. He told me the Team USA Trials. Problem was this player was invited, but got sick and did not attend the USA Trials. Of course, his name was still listed on the roster sheet. We quickly realized that this agent had not only never seen the player he wanted to represent, he in fact, was a liar! Needless to say, the player ended up going another direction.