Dual agency is a fiduciary responsibility that a single brokerage shares with both a buyer and seller. In other words, the buyers Realtor and the sellers Realtor have their license with the same brokerage. Now, if they are actually two different Realtors with two different clients, it isn't a problem. Each Realtor is representing their respective client.
Where it gets dicey is when the same Realtor is representing both the buyer and the seller. In some states, this is illegal. In others, such as California, it is legal. As with all things, this type of dual agency can be done ethically or it can be an unmitigated disaster.
An ethical Realtor will know where the line is drawn and what may and more importantly, may not be shared with their clients. When they are with their sellers, they will make an argument for a fair price that will satisfy the seller. They will work diligently to have a fair resolution to repair requests. In other words, they put on their "listing agent" hat. When they are meeting with their buyers, they work towards an offering price that their buyers are comfortable with. They go over the inspection reports and deduce what items are fair to be on the list of repair items.
Note in all of this, fairness is mandatory. It does become more difficult when one of the clients or both don't have the sense of fairness that their Realtor does. In this case, it is incumbent upon the Realtor to do advise their client, but then do as their client asks. After all, the contract and the request for repairs are agreements between a buyer and seller...not the Realtor or brokerage.
Ethical Realtors can go to great lengths to ensure the correct approach to dual agency. Sealed envelopes containing all offers can be asked for by the listing Realtor and brought to the seller prior to opening. If there is any question as to appropriate representation, the Realtor can ask their broker or another Realtor from their brokerage to step in for negotiations.
It is a fine line, but can be done correctly and result in a great experience for all involved.