A Business blunder

So...today I was selling at a craft fair, and some girls I know came to my table. I was saying hi to them when I heard an older lady, also standing at my table, say to her friend, 'She just keeps on yapping and yapping' Obviously loud enough for me to hear, so I turned to her and said, "I'm sorry, can I help you with something?"
She looked at me, slammed down the product she was looking at, and loudly said, "NOT ANYMORE" and she and her friend stompted off.

Well, I'm hardly one to be rude to anyone, especially to a customer....but I don't really know how I could have done the right thing here. I didn't know she needed help, or had a question. I find shoppers prefer to browse without me trying to shove products in their face. I guess my fault was being friendly to the girls I knew at the expense of someone else.

Now, I know this doesn't seem like a big deal, but I really take things like that personally, because I'm really not a rude person, and feel really bad that I didn't see her there. It kind of put a damper on what was otherwise an Awesome market day!