Yes yes, we all heard that before. The million-dollar question is why should people trust you and blindly send bitcoins to a stranger? I or anyone for that matter could hire coders to build a mixing site overnight and have it up and running in a few days but that alone will not make it a legitimate mixing service. The core question is about trust.

You should use escrow to ensure and guarantee that people will get their coins back. Nobody will trust fly by night mixing services.