I have many friends who operate antique shops, and often, while browsing through their ware, I've overheard obnoxious customers try to browbeat their way to a good deal.

My advice to my friends is:

Never welcome a person who has taste but who does not have the money to buy what he wants. He is in his personal hell and deserves to stay there.

He will only:

--pretend to be interested in something else while inching his way toward the item he really wants.
--eventually zero in on what he wants and tells you everything he thinks is wrong with it.
--haggle tirelessly over the price below realistic levels.
--be offensive toward you in an effort to demonstrate how much more knowledgeable and intelligent he is.

When you encounter such a customer, take the item, move it away from him, stow it away so that he can no longer see it, and say, "I changed my mind. This item is no longer for sale."

And don't even apologize for anything.