When a client says "I am just looking," your next words are very important. You need information at this point, otherwise you are just throwing darts at a wall of balloons. Sandy Shores commented above that she asks "How long have you been looking?" This helps to qualify if this person will truly waste your time right off the bat. The first comment by Cameron is also excellent.
The right questions are important here, for they can create a dialogue that helps to develop a relationship, and that all important trust factor. If they like you and you don't intimidate them, they will open up to your questions.
What are your trying to find out? Let's change their sentence a bit to help. Let's drop the word "just," and add another word after the sentence...
"I am looking, BUT..." Isn't this what they are really saying? You've got to find out what comes after "but."
When you know what they really mean, which you learn by asking the right questions, then you can move forward. Isn't this what "Sales" is all about? Asking questions, listening to the clients needs, and showing them how to achieve the goal!
Maybe this blog should be about...what are the right questions to ask when a client says "I am just looking."
Your greeting has been mistaken for (or, recognized as) an attempt to begin a sale and has forced the customer to exhibit evasion tactics similar to those in a predator/prey encounter. Quickly, they state “No thank you, I am just looking.”