The only way to know for sure is to send a hypothetical email to get an opinion in writing as to the tax liability for boat sales.
The local government tax collector for locale in which the boat is moored.
The state tax collector / department of revenue for the state in which the boat is moored.
Finally, the state agency that registers all boats for the state in which the boat is moored.
In Louisiana, private sales between two individuals are considered non taxable. If a broker is involved in listing the boat, sales tax must be paid to the local government & state government---period. One must sign a document attesting to the disposition of the sale; trying to avoid the sales tax is fraud & if you get caught you're in big trouble. Also, gone are the days that you could register a boat in Delaware as an LLC and bring the boat into LA tax free. If the boat is used in LA, it has to be registered in LA, regardless if it is documented. When it is registered in LA, you must prove that sales tax was paid either in LA or in another state. The Delaware LLC is not going to "hold water" any longer. Again, the only way around the tax issue is to arrange for a private or casual sale between two private individuals without broker involvement, in LA.