If your agreed value is greater, than what you are getting offered, that's going to be the way to go. You can try haggling some more with the other insurance company, but at some point, they will often ask if the boat is insured, if so for how much. Your insurance carrier will pay you out on the terms of your policy and go after this insurance company for their money back. You are going to get whatever the latest policy shows for the agreed value because that is what the premium is based on.