Obviously theres nothing to stop you putting in a low offer initially , but once an offer is accepted then the survey may pick up a few bits and pieces which you can then haggle further on. But I think the general rule is that the price should reflect the 'known' condition of the boat - i.e if you buy a 10 year old boat you can't really expect to ask for a discount because the survey says the sails and rigging are 10 years old. However if the survey says that something else needs replacing which wasn't know about then you can expect to have that either replaced, or taken off the price.