This is an interesting topic and so I'll add my perspective. I agree with Christina and think Dual Agency is very much a positive for both buyer and seller and this is supported by the comments below.
For example, Mark suggests Dual Agency doesn't work as the sale of a business is more complex than selling a home. This is the reason Dual Agency does work because Mark is correct, the sale of a business is much more complicated. Without fail, the only reason a business or most transactions get done is due to good communication. If the communication is poor then the result will be poor. When communication takes place with many parties it tends to break down. Email is probably one of the poorest forms of communication.
The benefit of Dual Agency is that one broker is the pivot between all the communication between the buyer, seller, landlord, lender, attorney's, CPA's and more. If there is a misunderstanding and the broker knows what they are doing, this will be caught and resolved.
Probably the greatest benefit of Dual Agency is that the broker is the party representing the business. That is, the business can't speak for itself as no one is supposed to know the business is for sale except the seller and the buyer and disinterested third parties. The broker wants to get a deal done as quickly as possible if the buyer and seller want to do a deal as they know that the business is vulnerable while their are negotiations and its therefore in limbo.
As a Certified Business Broker I really don't care on how much the buyer pays or the seller accepts - that's their decision and responsibility. My responsibility is to disclose EVERYTHING so that a motivated buyer and a motivated seller knowing the full facts of a deal can decide if they wish to do a transaction.
To Timothy's point, I am not serving two masters. I am serving two customers. There is only one Master which is the business and I see my role as protecting it and making sure if no deals get done, the business is in the same condition as when I was hired to try and sell it.
I also agree with other comments that a bad broker is a problem. This is the reason to look for a Certified Business Broker as they have training and certification to support their skills.