Bama and Derrick make a lot of excellent points. And I mean a LOT of excellent points.
Two tips that I can add:
1) Always play a couple dealers off each other. Even if they are different manufacturers. Make the dealer EARN your business. It's not what someone else paid, or what you see on seedealercost, it's what you can get that one dealer, in your area of the country, to actually agree to sell you a boat for. It doesn't matter what seedealercost says if the dealer ain't selling a boat for that. Like Bama said, area of the country matters. His volume matters. If you're out in the sticks and he doesn't sell many boats, guess what? For example, early on in my negotiation, I was dealing with just one dealer until he obviously got tired of me (I'm sure you guys can relate to that! Okay Derrick, there's your opening...) and he told me he had given me the BEST price I will ever get on THAT boat ANYWHERE. EVER!!! I still have the email. It makes me laugh every time I see it because I took that as a personal challenge, and promptly went online to find the next closest dealer. And guess what? He was wrong. I got a better price at another dealer. I also got a dealer I like, trust, respect, and will go back to in a heartbeat. HAVE PATIENCE. GET TWO DEALERS.
2) USE EMAIL! Car dealers and boat dealers make deals every day. They are VERY VERY good at it. You (and I) would be that good too if we did it every day, but fact is we don't. That's not a fault, it's a fact. We do it once every few years. That's FAR from every day. In order to overcome your shortfalls, you have to recognize them. I, personally feel like I am at a major disadvantage in a "live" negotiation. I've walked away from many deals because it just felt like I was getting snowed. The other guy (used car dealer) knows all the tricks. I feel like I'm fighting my way out of wet bag. EMAIL slows everything down so you can THINK about what's happening, you can THINK about the message you are sending, and THINK about what you REALLY want to say next. I'm not kidding, email REALLY levels the playing field. Instead of having seconds to respond (as in a face-to-face conversation) you have all day to think about it if you want. Start with an in-person visit to the dealer so they know who you are, but negotiate the deal via email. That's my advice. I'm sure there are others that would disagree, I'm just sharing what worked for me.
I do understand, though, that you want a target price. We all want to use every tool to get the best deal we can. If you trust seedealercost (I don't see any reason not to, but I'm not familiar with it either) then that's your target. Print the thing off and bring it to your dealer. Write out a check for that amount and give it to him. That's a great starting point. Always better to make him negotiate up from that price instead of him making you negotiating down from MSRP.
2 cents. Maybe.
By the way, ever watch Pawn Stars and other similar pawn shop shows on TV? EVERY time they start the negotiation by saying "What are you looking to sell it for?" They ALWAYS make YOU name the first price. They make you bookend yourself right off the bat. Great trick. You can learn a lot from watching those shows if you don't do this every day. They also often simply say "I just can't do that" and they don't say anything else, and they just sit back and see if you take the bait and fight YOURSELF on the price! It happens every show! Watch next time and you'll see. Some idiot keeps lowering his own price, and the pawn shop guy (or girl) just keeps saying "no" until the customer starts to get close to his real target price. Brilliant strategy. Simple too. Those guys are pros. Where else can you witness a "used car" negotiation as a proverbial "fly on the wall"? I'm telling you, watch those shows, and pretend your buying a car or boat...