I worked for a new boat dealer in the UK and the margins were tight - he had around 14% to play with. The usual line was to offer extra 'options' rather than discounts to start with. Even so, you could get 5% off fairly easily and more if you pushed a bit. Very occasionally, he would forgo the full 14% to get a boat off his books
to get new stock in.
All dealers had their 'areas' and no dealer could officially poach a customer from 'their' area. There were several bun fights but they generally stuck to the rules. As a buyer it's best to be vague about where you're from, then you can get quotes from several 'areas'. Be careful though - they do talk amongst each other, and if they think you're being sneaky they get upset.
I also had a mate who worked for the Sunsail sales team. He said the best time to buy ex-charter in Europe
at least was late August as their bonus year ended then and they were desperate to get boats off their books
and very large discounts could be negotiated at that time.
Playing the currency game
can also net a large discount - Although I've seen my £sterling boat budget
shrink about 10% in the last few weeks
Hope that helps!