Many artists have a lot of sales experience, and know this stuff, but a lot of artists are new at selling. Before becoming a full time artist, I spent several years with a high tech company selling at trade shows, and attended a few sales seminars during that time. I would like to share a couple of things I learned and practice that are guaranteed to increase your sales.
Always greet your customer - When a customer walks into my booth, I stop whatever I am doing, stand up, smile and say "Hi, how are you today?" I learn a lot about the customer by watching their body language and by hearing their response. If they frown, say nothing or say "I'm fine" without looking at me, that usually means leave me alone, so I let them be, but if they turn around and give me a big warm smile and say "I'm just having the greatest day", that's my cue to take the next step and try to start a conversation.
When they leave, even if they don't seem interested in your work, smile again and say thanks for stopping by or something similar. Just because they didn't stay long or say anything doesn't necessarily mean they aren't interested in your work. Often they go around and look at everything before they make a decision, and they return and buy something. I have had that happen many times.