The amount paid to Business Brokers is always negotiated between the Seller and the Broker. Most charge a straight percentage of the sale price, paid at settlement. Some charge up-front fees, some do not. It is not an easy question to answer, for that reason. And state-by-state, region-by-region, there are differences in the local commission culture.
The Broker's commission is normally higher than commissions charged by Real Estate Agents, because a Business Broker works in different ways. The biggest difference that causes the higher commission rates is in the nature of the confidential way the Broker must work. We cannot, for example, simply but a sign in front of your business, or place the business in a multiple list system where other Brokers can easily identify your business, and drop by with Buyers, almost at any time. There is no lock box with a key, allowing other Brokers to come in and show the place in your absense. Selling a business is not like selling a house. With a house, it is the physical setting that is important; with a business, it is showing financial records and explaining the nuances of your business that is most important, which means your Broker is always involved, in a very personal way.
Because of the confidentiality that the vast majority of businesses require, the Broker canno be a passive promoter of your business. He/she must take every call, sift through every prospective Buyer and inject him/herself into every potential contact. Compared to a Residential Real Estate Agent, each transaction is incredibely more time consuming, and no responsible Business Broker can adequately represent his/her Sellers if he/she takes on too many listings at any one time. (By the way, I am NOT criticizing Residential Real Estate Agents. The difference is not a question of which is better or more intelligent; it is simply a matter of different skils and the methods of promotion that each employs.)
The Broker can work with you to determine the price that you can anticipate. He/she should work with your Accountant to make certain the Broker understands all of the financial circumstances that surround your business. Your bottom line may be over or under the price that can be anticipated. I am working with one Seller that said he would accept no less than $3 million; it has taken me a year to get him to understand that the business was worth no more than $2 million. In another situation, the Seller initially told me he wanted $250k for his business, and he would be happy; we got him three times that amount!
Most small businesses have pricing that is based on Cash Flow. The Broker that represents you is paid out of what you accept. If a Buyer's Agent is paid out of that commission, it does not affect your bottom line - it comes from a split with your Broker. But be away that most Brokers do not share their commissions, which is something that I personally believe works against you! You should clarify that with any Broker you interview.
And you should interview them. Try to get referrals from other business Sellers who have been satisfied with their Brokers. If you don't like the answers you are getting, if you do not believe the Broker is being responsive, DON'T SIGN A LISTING WITH THEM! If they are not treating you well before you sign the listing, they will certainly not be any better after the fact!
I hope this helps. Good luck.