I don't think the agent is saving much, if anything. That agent is entering into a dual agency role, which is not always a good place to be. It is very difficult to represent your interests and the owner's interests at the same time. Many agents won't accept such an agreement.
There are no set fees or "standard" commission amounts. Make a proposal and see if it accepted.
I have offered discounts to repeat clients of 1% to 1 1/2% (from a 6% listing) for a repeat sale.