To begin with, let me say that "hire a designer" is not really an answer. Problem is, I will still have to evaluate and accept or reject whatever he or she creates. Personally I would go with a totally minimalistic design, but I bet many would consider it amateurish. I don't want to risk losing customers just because my personal taste is not very mainstream.
Where to get an idea what "modern", "professional" and "trustable" mean these days?
take a look at themeforest.net for an idea. We got our templates and images from them and their sister sites.