Instead, please consider calling 3-4 local agents, as part of the interview ask how much they charge for the transaction. I assume you are talking about listing your home, correct? Becuase if you are buying, most of the time if the property is listed for sale on MLS, it will not cost you anything to use most agents or Realtors.
If you are selling, once you speak with 3+ agents or Realtors, I am confident you will have an idea of what the "average" or "Standard" charge is. In short, each agent can charge whatever they want, and it is up to you to agree to it or not. However, you will see what most charge after speaking with just a handful.
Best of luck.
The previous answers below are all correct, especially Spirit's in regards to anti trust laws. Since you are listed as a home buyer, I'm going to assume you're talking about the additional fee (broker fee, transaction fee, or whatever they are calling it in Philly.) The same answers do apply to that fee as well. Meaning it is negociable, if you have an agent that you know is going to save you over and above that fee, it's well worth it. If the realtor is just letting you in the door and leaving the negociating up to you, then practice that negociating now and get that fee to zero. They will still get their commission from the listing agent of which they will just have to gather the transaction fee from that.
I don't work in the Philly area, but do know several good agents that do. If you'd like help negociating that fee to zero give me a call or email and I'll gladly help.
Hope this helps.