I've had this kind of thing happen to me in the past. I can't recall what I was selling, but the situation was the same. It may have been even $10 less than what I countered with. I just replied, Do you want it or not?
I sort of treat every negotiation on a case by case basis. If someone is nickel and diming, but is not far from my price, and they seem like they're going to be a hassle to deal with, I just pull the plug.
I've had people make offers that were a little lower than I wanted, but were easy to deal with, and were coming a long distance to get the item. That's when I'm more agreeable.
When I'm looking to make a purchase, if I feel the asking price is fair, then Ill make a reasonable lower offer. If they counter with their asking price, and it's an item I want, then I have no problem just paying it. We're both winners.