I don't see why it was such a big deal for the agent to tell the other couple the flight was oversold. Seems wrong to me, but I wasn't there. I've seen GA's be completely honest with pax about the cause of a delay (i.e. weather, ATC, anything else out of UA's control) only to have a the pax tell the GA that he/she was lying to him. If agents continuously are being told by pax that they are lying, then why not make up a story to avoid confrontation to begin with.