In Europe, broker gets 10% if he achieves the asking price. Which means almost never. If the selling price is negotiated, usually the commission is negotiated as well. Usually, this means that the broker will end up with 5 to 8%. And it makes sense: if the owner makes an effort on the price, the broker should make an effort on commission.
On new constructions, shipyards will usually give 5% although some are now starting to offer 10% to attract brokers and encourage them to offer their products to customers.
On very large stuff, the scale goes as follows:
10% on the first $ 10 000 000 value
5% on the next $ 10 000 000 value
2.5% on any value over $ 20 000 000
So you can hope to get 10% only on stuff under $ 10 million.