[benj111]

>I heard that they don't clean the dishes enough

Is that defamation? That isn't a statement of fact, that's just relaying what you heard.

If I relay what the Daily Mail says, am I also guilty of defamation, or can I rely on what others say?

[SoftTalker]

If you quote the Daily Mail, with a citation, then probably not. If you are repeating a vaguely-source rumor that "you heard" then that's heresay and could be defamation.