It should be obvious. The guy who shows up to your intro meeting well-dressed, prepared, etc with references is going to be preferable to the guy who shows up smelling like vodka in tattered clothes.
> As a merchant, what if I have no reputation? How do I ever get my first customer?
The same way you do under the current system. Go work for someone else to build up credentials/experience, or, offer to do stuff for free in exchange for referrals and testimonials.
> on a centralized platform that can arbitrate trust!
Can, but often doesn't need to.