I just finished a successful show and learned a couple of things. I changed some of the things I had done in the past. The first change was how I approached people, well actually I did approach people. My observation has been that artists tend to hang back, hover at the desk area and mumble something like "oh I'm too shy".
I never worked as many shifts as I had this time and I think it helped me quite a bit. There's no point to working a lot of shifts if you sit a the desk and read a book.....duh. I had the opportunity to practice my blurb about my work on real people and refine it according to the reaction they gave me. An added bonus is that there are a lot very interesting people, take the opportunity to talk to them.
I approached people and asked them how they were doing....waited for a response.....delivered the appropriate rely....then told them I was one of the artists in the show and be sure to come to me with any questions. That gives them the choice to talk or not. People like to feel they are in control, so if they just thanked me I left them alone. It's always good to follow up with the people who made a purchase after the sale as well. I started my follow up after the sale with a question "have I answered all your questions" sometimes I hadn't.
One thing that I haven't quite figured out is when people tell you how much they like your work (blush blush) and I have thanked them, sometimes following that, is a short awkward silence...humm. I think I need a couple of good follow up questions which might get them talking again.
You probably shouldn't approach people with the idea that everyone is a sale. I noticed that not only do people want to control the amount of time you have with them they also want a bit of space. Best to just answer the questions they have and get to know them a little. It's interesting to note what they like about your work, sometimes it's something you wish you would have changed before the show and it's the very thing that they love. Awesome!