From the Godfather:
And don't in any way quarell with him. Tell him you have to get the money and you will give it to me to give him. Let him understand that you are willing to pay what he asks. Don't bargain. I'll quarrel over the price with him. There is no point making him angry if he's as dangerous a man as you say he is.
They left it at that.
The last sentence, what does that mean? How could we use that construction in another case? The phrase Left something at that is common in modern English, huh?