Dennis:

I am with the Silicon Valley Bicycle Exchange. We have an explicit conflict of interest policy designed to prevent volunteers at any level from profiting from their volunteer activities.  Removing the incentive of personal financial gain helps to see that volunteers are taking more responsibility for the right reasons. 

Our shop leadership is mostly self-selected volunteers who show up at our steering committee meetings that happen every other month. From this additional time commitment and willingness to take action items it quickly becomes evident who is a committed and trusted volunteer. 

Responsible leaders are developed, not born. You should be taking steps to meet and get to know the volunteers to decide which ones you trust. Remember their names. Make them feel welcome, continually remind them of your shop’s goals and organizing principles. Invite them to incrementally assume more responsibility. 

I got drawn into a leadership role at my shop when I observed how hard our leader was working, and asked if there was something I could do to help share the burden.