When I mail ordered my Dell computer from Texas, I had to pay
Massachusetts sales tax. I think Massachusetts has a law but it
is only enforced for big ticket items like computers -- and
especially, automobiles! (If you buy a car out of state, and
try to register it, they'll whack you for the tax.) Dell may
have offices in this state, so that may be the key.

I've never paid MA sales tax on an out of state freight car!

Tim O.