I can work both modes that is hourly or fixed based. First of all I required a very clear instructions and requirements of your project/task to complete. After I analyze and put an estimate containing cost and time to complete project.
I usually break project into milestones. 10-25 percent of project cost has to be upfront mean paid in advance, for security purpose. It make sense that you are serious and want me to work for you. You must not worry about that upfront as upfront is reversible if we cannot continue to project for any reason.
More ever as I work in very frank style, so my clients get familiar and easy with me very quickly, and this creates a better trust for our long term business. I happy that my every coming client may be my long term business client too. And hopefully this is what every client thinks too, that he should use one trusted platform/company/person to get rid of any type of future fraud that are common in this field.