The short answer is that - we don't.
GoRevival is a site where Christians help other Christians - so our hope is that our members are men and women of their word and carry themselves with integrity and honor.
That being said - unfortunately sometimes circumstances and life can interrupt our plans. Morning alarms don't go off, traffic is gridlocked, work ran late, family emergencies - sometimes things happen that are out of our control. Please have grace in some circumstances.
We always want to assume positive intentions if someone is unable to carry through with their commitment to serve, however if someone is notoriously absent or negligent in their service - GoRevival would appreciate if you would report it through the site. We want to make sure that there is an atmosphere of integrity, especially in regards to service.
We recommend that for extremely important or technical needs - consider hiring for your need or have an in depth application process for the volunteer.