In Act II, scene iii of Much Ado About Nothing, Benedick says in his soliloquy:

May I be so converted and see with
these eyes? I cannot tell; I think not: I will not
be sworn, but love may transform me to an oyster; but
I'll take my oath on it, till he have made an oyster
of me, he shall never make me such a fool.

Benedick is speaking of Claudio, who is a romantic fool in Benedick's eyes.  Benedick is asking the rhetorical question, "Will I be changed like him, and see the world through a lover’s eyes?  I don’t think so."

The irony, of course, is that he will very soon be "converted" by Don Pedro, Claudio, and Leonato, not by his eyes, but by his ears: he will overhear their conversation about how much Beatrice loves him.  He will immediately become a romantic like Claudio.

Later in the scene, Margaret will say to Beatrice:

Moral! no, by my troth, I have no moral meaning...Yet Benedick was such another, and now is he become a man: he swore he would never marry, and yet now, in despite of his heart, he eats his meat without grudging: and how you may be converted I know not, but methinks you look with your eyes as other women do.

In the same scene, Beatrice will be "converted" by her friends as well.  In short, both Beatrice and Benedick, previously skeptics of love, will begin to look for signs of love from the other now that their hearts are receptive.  It seems they have been attacking each other simply to mask their love in denial.

This quote reveals the themes of "appearance versus reality" and "love versus jealousy."  How do we perceive love: through our eyes or our hearts (feelings), or both?  Shakespeare, a romantic at heart, seems to say it is a matter of perception and an inevitable human impulse.  At the very least, it is a good recipe for comedy.

Remember, Barachio and Don John will deceive Don Pedro and Claudio with both ears and eyes.  During the masque, they will tell Claudio that Don Pedro is wooing Hero for himself, and when that does not work, Don John will show Don Pedro and Claudio that Hero has been unfaithful (Hero's supposed affair with Barachio, but it's really Ursula).  So, the eyes can be converted to jealousy and hatred just as easily as love, a major duality in the play.

So, do we believe a lover's actions or words?  Since both can be used to deceive, it's a risky proposition, but that is the "leap of faith" that love presupposes.  As you know, love is worth the leap.