Here is a little information from US Customs and Border Protection:
https://help.cbp.gov/app/answers/detail/a_id/1184/~/importing-a-boat-for-personal-use-into-the-u.s.I don't think the EPA requirments mentioned would be any issue since the boat was manufactured before 2010. (and also produced in the USA for USA use, and has appropriate USCG and NMMA tags) But there is still a form to fill out.
A 1.5% duty is mentioned. I don't know if this applies to a used boat, especially a USA made boat, but a call to Customs and Border Protection could tell you for sure.
As usual, in most states, sales tax would apply to the buyer when he registers the boat.
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"Knot Easy" 2000 Horizon 240 Volvo 5.7GS /SX
tow: 2017 Honda PILOT EXL-AWD
prev. boats:
'87 Chaparral 198CXL 4.3 OMC Cobra
'69 Jetstar 16ft Ski Boat, 115hp Yamaha
'68 Aluminum Jon Boat, 3hp Sears
'64 Water Wings