ALWAYS wipe your equipment before you sell it to anyone.
This includes things like hard drives and network devices.
I can't mention any names at all, or specifics, but I ordered a couple of refurb routers a few days ago, and I was very surprised today when I saw full router configs in place, complete with IPSec settings, ACLs, and plaintext read/write SNMP strings.
Always wipe your configs before you sell the devices. Always.