1
general::
Something attractive is not always what it seems, as in This house is really beautiful, but a close look will show dry rot near the foundation? all that glitters is not gold. Aesop stated the same idea in two of his fables (c. 600 B.C.), and a version close to the current wording appeared in 1175.
American Heritage Idioms
2
general::
Phrase(s): All that glitters is not gold. [and] All that glistens is not gold.
Prov. Just because something looks attractive does not mean it is genuine or valuable. (Often said as a warning.) • Hollywood may look like an exciting place to live, but I don’t think you should move there. All that glitters is not gold. • I know Susie is popular and pretty, but don’t be fooled by that. All that glitters is not gold.
McGrawhill's American Idioms And Phrasal Verbs