Vermont also asks residents to voluntarily report any taxes owed on internet or mail-order purchases.
There was a story from last year that detailed a resolution that was being considered by the Massachusetts legislature that would demand that merchants in New Hampshire (or, it might have been RI) ask for proof of residency from their customers, and then collect the MA sales tax from the customers that were actually from MA.
Yes, you read that right - MA wanted to pass a law demanding that NH retailers do something. That's how crazy they are in MA. Of course, NH told them to go (%*^& themselves, as they should have.