Commission rates can be negotiable but when you sign the listing agreement it is for X$ commission. Insert whatever the number is. (Typically 5-7%)
In virtually all listing agreements it says they will share some percentage of that with the buyers agent. Typically but not always that is a 50/50 split. But if the listing agent sells the home directly ther is no split and you still pay the full amount of X$ commission. That listing agent just hit a "home run"!
Variable rate commission changes that. It says that if the listing agent sells the home directly then you will pay less commission. many agents do not even know what variable commission is and many of the brokers will not allow agents to offer variable rate anyway.
I have been offering variable rate commission for 10+ years!
When you list with Atlas Realty Service the listing side commission is 1% and buyers side commission is 3% for a total of 4%. However, if I do sell the home directly to the buyer then the total commission is reduced to 3% so you save even more!