Negotiating sales commission

This goes back to 2008 when home prices were dropping. I was POA of my parents estate and put their home in Sun City West AZ for sale. The home sat for sale for about 8 mo while the value was dropping like a rock with no potential buyers. I looked online and saw there were similar homes selling in that area. I called my agent to see why it wasn't selling. She said yes there were other homes selling but just didn't have any serious buyers for mine. Then she said, you know your sister made us drop our commission 1%. I got pissed because she had no right doing that. I told the agent, you know, if i'm selling homes and i can make 1% more on this one verse that one, which one i'm i going to push. She followed with, don't make me answer that. So i said, you got your 1% back and i will give the agent that sell's it a $1000 cash bonus. She said thank's for the 1% back and hold off on the bonus and give me a bit to try and sell it. 2 weeks later it was sold. I wasn't going to tell my sister but when i told her it was sold she started bragging about getting the 1% extra. I explained it to her then along with how much the house had depreciated while it sat on the market. Expensive lesson.