I am an artist and regularly do business at art fairs in 4 states, including Michigan, and am familiar with this problem.
The rule is that you have to charge the sales tax of the state in which you make the sale, and send it in to that state's Dept.of Revenue. You also need a merchant's license for each state that you do business in, and can find the info about that in each state's website.
However, I did an art fair in New York once, and simply charged the NY tax and mailed it into the NY Dept. of Revenue with a note that it was a one-time only event for me. I gave them my home state merchant's license number and they cashed the check and I had no problems with them.
I always feel that the main thing is to be above board and do the right thing, so nobody can try to get you in trouble.