How about this for start. Other than the obvious don't let on to how much you've got to have the boat, what are some couple other do's and don'ts while playing the sales game?
One thing you can haggle on is, If you are financing the boat with the dealer ask for another discount. They normally get a kick back from the finance company.
If the boat is not in stock, remind him that he will have no interest on the boat as you will buy it upon delivery and setup.
We recently took a day off and drove 200 miles to look at a new Tri-Toon, Then had an appointment to look at another 215 miles from there. I texted the saleman we were running late and got a phone call when I was about 30 miles from there they sold that boat the night before. I let him know my disgust and that I thought a phone call would have been in order! I also told him we had left home that morning and still had 240 miles before we could lay down that night. I went on to dealer as owner said he would order us one and give similar pricing as the advertised deal he had. We haggled for about 2 weeks via phone and email and feel as we got a really good deal. (Scary, I know) BUT we have on order a 2017 Avalon like we wanted it, and a build date in March. This is with a 200HP Suzuki and are paying less for it than quoted on other boats locally with 150HP engines and less extras. I used both of the above tactics and wrangled the deal where he showed me credit for trading in my old boat and him selling it to the buyer I had on the hook for it. Saved me the Sales tax on my trade as well.
Good luck and get what you want if your buying new!
On a side note about used boats. The Tri-Toon market around my area (W. Tennessee) is very good. I was able to buy a new boat from a dealer for less than $1000.00 difference of what used boats were going for.