i spent 6 months haggling on mine on an already good listed price and got about 15% off. others get a lot more off the listed price.
good to remember 3 things, you can always go up with your offer not down, the broker will always want an offer - any offer, and the things are easy to buy and hard to sell.
imo, doesnt hurt to come down 30% and make offers on several boats at once. plenty of brokers know each other, and if they talk, they will see you are real about each one.
there are some good heads here so im sure some sound advice will and has been put in