You asked this in "New Hampshire Laws", so the answer under NH law is: none. Cash and carry.
BUT... since this is an interstate transfer, federal law requires that it go through an FFL. I assume you can't legally possess the long gun in MA, so either the seller brings it to a NH dealer for the transfer, or has it shipped to your NH FFL for transfer. All FFLs charge fees for these transfers, and it's worth shopping around.
Clearing this in advance with all FFLs involved is highly recommended to avoid wasting gas money.