The only thing really negotiable is the price
of the charter and first night sleep aboard fee. Most companies will drop the charge for first night sleep aboard fairly easily. As for the charter fee it depends a lot on how many boats the company has that aren't yet booked, the state of the economy, the length of the charter and whether you've had a prior relationship with the company. Another factor is the time before you booking and sailing. The shorter it is, the more likelihood you'll get a better price
. In other words, a last minute charter gives you an advantage as that boat would probably just sit on the dock
making no money
Most of the other stuff you mention is covered by very, very small print in the charter agreement. Remember they always have the full cost of the charter before you get there so there is little you can do over a poor boat, breakdowns or, as has happened more than once with smaller outfits, no boat!