Jons right, general reseller support responsibilities are setting up clients accounts, giving advice and fixing things that can be done from a reseller control panel. The main responsibility is making sure you give the right advice, so that could mean emailing your host to double check their answer with your answer. Your host is usually responsible for keeping the server online and stable, installing modules, scanning for 'foriegn files' and anything related to a reseller account such as upgrades/downgrades, reboots/service restarts etc.