Dual agency or double dipping is an agreement between a realtor and two other parties. If the buyer clearly states that they are not being represented and no dual agency exists, on the contract, and they have signed no such dual agency agreement with the listing agent, then no dual agency will exist. Therefore, the agent cannot take the commission allotted to both agents.
The commission allotted to a Buyer's agent is not solely an agreement between the listing agent and the seller. It concerns the buyer as well. The buyer must agree, assume, or otherwise understand that such a situation will arise. However, if the buyer refuses such a situation, and does not wish to be represented, then no such dual agency exists, and no such commissions will be paid out.
Let's make this simple, shall we. Show me in the contracts you sign with your clients that states otherwise. Do your contracts suggest otherwise, and if so, please share the them (hiding confidential information of course).