Ever been nibbled by a customer? It’s not as rare (or as fun) as it sounds. Just when you think you have a deal with a customer, she asks for “just one last little thing." This is referred to as “nibbling."
This usually isn’t a deal-breaking request; the customer simply has to see how far they can push. This is particularly common with customers who like to think of themselves as tough.
“I just paid all this money for the copier. Surely you’re going to give me some toner for it too” might be an example. Smile and reinforce the fact that you just negotiated a fair deal. Do they really want to complicate things now? Usually, the customer will stick to the original request.
If you do have to give up something, ask for a small concession from them first. A solid referral is not a bad trade in some cases.