See generally LSJ s.v. agoraios (web address 1) for texts further illustrating both of these disparate senses (and note the comment there: "the distinction a)go/raios vulgar, a)gorai=os public speaker, drawn by Ammonius [a C1/2 grammarian] etc. is probably fictitious"); cf. alpha 309. See further D. Whitehead, Hypereides: the forensic speeches (Oxford 2000) 287.
[1] Likewise or similarly in other lexica; references at Photius alpha233 Theodoridis.
[2] Aristophanes, Knights 297-8 (web address 2: the manuscript reading is "I perjure myself before those who are looking"), with scholion. The same epithet is attested, elsewhere, of Artemis, Athena and Zeus.