It's very simple. The answer is no. The negotiations are done.
If he is concerned that you are going to rip him off, then you can find another way to satisfy his concern. With milestones, payment schedule, delivery of source code for him to inspect, etc.
If you can't find a way to satisfy him in a way that makes sense for you, then don't do the job. This world is filled with millions of clients which are less trouble and more sane. Kick him to the curb now before he causes trouble later.
One of the main benefits of freelancing is that you choose who you work with. You don't work with every person who says that they will pay you. You work with who you want to work with. If you don't like them then tell them no.