Firstly, check your calendar and see if you have availability before accepting. Make sure all the details are correct. If you want the renter to know about any extra costs associated with the rental that are not included in the ad, such as fuel and the cost of a captain, it’s better to inform them before accepting the request.
If it's because the boat is not available, this article may interest you : How to update my calendar? How does the import of external calendars work?
By clicking on "change the dates, the rates or the boat" you'll have the possibilities to offer new conditions.