The seller and the listing broker have an agreement that the seller will pay the listing broker an agreed amount and then the listing broker has agreed to pay the buyerâ€™s broker as per the agreement of the MLS.
There is a misnomer that there are two commissions one for the listing agent and one for the buyerâ€™s agent. To reiterate there is one commission paid from the seller.
The amount that is paid between the brokers is a separate agreement.
The theory is if you offer an agent more then it will be shown more. Which IMO cannot hurt to get a home shown. However I do not think it will sell an overpriced home.
BUT, it does indicate that they are pretty serious about selling the home.