My number one most important rule for my behavior during an art festival:
Make every single person who walks into my booth feel welcome, and glad that they did.
This is easier said than done. Art festival work requires some advanced people skills. You cannot fake being comfortable with people, you need to BE comfortable. Festival artists are "on stage" to some extent. Your booth must give off positive happy energy, and it needs to come from you. For 6 to 8 hours straight per day. And again, you can't fake it. It needs to be genuine. I credit my years of teaching, this is where I developed my ease with talking to people, including total strangers.
This does not mean I am talkative with customers. I do make a point to greet everyone, but I do not engage in conversation unless I sense that it's appropriate. When needed, I have plenty to say about my pottery.
When somebody leaves my booth without buying anything, that's ok with me. And I let that person know it's ok, with a "bye" or "thank you." The fact that they walked into your booth means they liked your work. If the visit was pleasant, there are lots of sales to be made later. But if you burden someone with your disappointment, that person is gone forever.
When somebody makes a purchase, I will make sure that they know how much I appreciate it. And then there's another level to this, when customers become repeat customers, I make a point to learn their names and recognize them as repeats, and show my appreciation.
Overall, the "fun and rewarding" part is that people get to meet a friendly and happy potter, who clearly loves her work, and made them feel glad about going to the art festival.
The really hard part is there are so many reasons to sink into a negative mindset at a show. If you want to succeed at this, you can't. I also visit and shop at lots of art festivals, and I'm afraid too many artists are falling short on people skills. Shyness and insecurity are very common. So is arrogance (ugh). So is desperation (double ugh).
The worst example I ever overhead .... the artist in the next booth, upon receiving a nice compliment from a customer, responded with nasty sounding "Well I'm really glad you said that because I'm having a terrible show!" Gee I wonder why???!!!! Can you imagine how awkward that poor customer felt?