In the 1970s, there was a TV show called Colombo, a Los Angeles police inspector in the homicide section. He would keep asking question and whenever he was just about to leave, by the door, he would say:
Oh, by the way, what about ...
You thought he was finished, but he would keep on and on...
I had this customer, almost everything was finalized with the when, the where, the how, and the how much then:
Oh, by the way, can we also include a 16" by 20" print?
I almost "flipped", he wanted it for free and included in the price. I gave him such a good deal, and he had the chutzpah1 to ask for more. After 2 deep breath, and counting one banana, two banana and three banana2 I told him:
Of course, it will be another $450 for the print, mounted. The normal price would be $750, and another $375 for the framing.
He tried to argue for less but I was firm and always came back to:
I already gave you...
Luckily, I was able to recover and not to take it personally. So beware of the "Oh, by the way...", unless you are on the other side.
1 Nerve, gall ↑
2 In the old time, cameras only went up to 1 second, so we would time longer exposures by counting the bananas. ↑