Still skeptical, you decide the Historian's Pen is definitely your best choice. If—when—this all turns out to be a hoax, it's the only one of the three that will actually be marginally useful, if only as an ordinary pen. Thus decided, you grab the pen and walk up to the front of the store, where the elderly proprietor is hanging a freshly-painted sign over the counter. After he hammers the last nail into place, he turns to you and smiles, gesturing elaborately at the elegant lettering which reads: 'Because I am a wizard.'
"So," he beams, "what do you think?"
You search frantically for a tactful reply. What to say to a grown man in a bathrobe claiming to be a wizard? You've suspected since you first saw his robe that this guy might be more than a little senile—if not actively insane—but you hardly want to say that, especially if it's true.
"It's… nice," you say.
"I most certainly am not!" huffs the old man.
"You're not nice?" you ask nervously.
"What? No, I'm not senile."
You take a step back. "How did you know—"
With a flourish, the old man points to the still-wet sign.
"Um… right," you say.
"Oh, I know you don't yet believe—that doesn't matter. I only mentioned it because you asked. Well, that and perhaps a little excitement with the new sign—but mostly because you asked. I used to have a rather nice one, you know, with embossed gold lettering and all that. I was really quite fond of it. Quite an unfortunate affair what happened. There were these luchadores, and—ah, well, never mind. It's a rather long story and I'm sure you have places to go. Now, what can I help you with?"
Luchadores? As in masked Mexican wrestlers? Whatever—the man's probably crazy anyway. Better to make your purchase and get out.
"So, uh, how much for this pen?" you ask, brandishing it.
"Ah!" he says. "The Historian's Pen! That's a very powerful artifact indeed. I trust you read the label?
You nod.
"Then you realize that with this pen cannot write falsehoods? That every sentence it produces is complete, irrefutable fact?"
"Yeah, I guess," you say, blushing. It sounds even sillier out loud.
The old man looks at you appraisingly. Finally, he nods.
"Very well," he says. "You may have the pen for sixteen dollars and seventy-three cents."
Emptying your pocket, you are surprised to find that you have exactly that amount.
"That's weird, how did you know—"
Once again, the old man simply sighs wearily and points to the sign.
"Oh. Right."
Handing him the money, you pocket the pen and walk hurriedly out of the store.
Once back out in the food court, you idly flip the pen over in your hand. Where should you try to use the supposedly magical pen? It is called the 'Historian's Pen,' so maybe you should use it in History class. You've got an important test tomorrow, and a pen that won't let you make any mistakes would certainly be helpful. You also have a creative writing assignment due next week—you weren't planning on starting it yet, but it would be a good chance to see if anything special happens when you try to write 'falsehoods.'
Then again, the label did say "use caution." Maybe you should test it a little before committing to anything large-scale, especially a work of fiction.