We use macs at work, and several people quit. When we assigned their macs to other employees, we couldn't update to Mavericks because our former employees had registered OS X with their personal emails! Is there a way to change the Apple ID tied to OSX?
You'd have to wipe the drives, reinstall the original OS the computers came with. If the iLife and/or iWork apps were App Store versions, you'll have to repurchase them, as they remain tied to the Apple ID that accepted them.