I've read on the Cozy mailing list or the Canard Flyers list that in Texas
it was sufficient to state that all applicable taxes have been paid for a
plans-built. On the same list, it was mentioned that Massacusets wanted a
sales tax on all materials purchased from out of state.

I called the state comptrollers office and was told no taxes were due
because this was an "occasional sale" which means neither the seller nor I
are in the business of selling stuff. I did explain the stuff in question
was going to be used for an airplane. Since I wanted something in writing,
they directed me to write an email to the comptroller's office, and I'm
awaiting their response.

So I suppose it depends on whom you buy stuff from... a retail outfit-taxes
due, individual seller-no taxes. I'll post the 'official' response when I
get it.