If you are selling items that are subject to Massachusetts sales tax, then you should be registered to collect sales tax. This is the case whether you live in MA or are coming from another state.
This document will tell you what is taxable and what’s exempt: http://www.dor.state.ma.us/publ/pdfs/sls_use.pdf
If you are not registered to collect sales tax in Massachusetts, you should do this online, print out the temporary certificate, and bring it with you on the day of the fair, just in case. In theory, state officials can come to craft fairs and ask people to present their sales tax registration.
To get registered to collect sales tax, go to this URL and click “WebFile for Business”: http://www.dor.state.ma.us
If this is the only craft fair you are going to do this year, you should be able to specify while going through this process that you only want to be able to collect sales tax for the month of June (for our Summer Fair) or December (for our Winter Fair). And this way they’ll only expect you to pay once.
If you don’t want to have to deal with tacking sales tax onto every sale you make (and thus have to have lots of coins for change) you could keep track of your total taxable sales and just send in 6.25% of that.
The Mass Dept of Revenue phone number is 1-617-887-MDOR if you have questions.
