1 Shady black market weapons dealer: Transfer your money now at this terminal and we'll deliver the weapons tomorrow.
2 Iki Piki: How do we know we can trust you?
2 Shady black market weapons dealer: You don't.
3 Iki Piki: Ah. This is one of those classic cinematic moments where we actually can trust the guy, but doubt is added for dramatic effect.
4 Serron: Yeah. I'd be more worried about whether he can trust us.

Have you ever noticed that? Whenever a protagonist asks, "How do we know we can trust you?" and the mysterious contact of unknown loyalties replies, "You don't," it's always the case that they are, in fact, trustworthy.

On another note, I wish I could remap my Caps Lock key to Deposit $1 In My Bank Account.

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2017-06-03 Rerun commentary: I wonder now what a non-trustworthy contact would say to the same question.

"How do we know we can trust you?"
"Oh, you totally can. I'm not going to betray you! Truly!"

"How do we know we can trust you?"
"Hmmm, good question. That does present a logical conundrum now, doesn't it?"

"How do we know we can trust you?"
"Because I have a Wikipedia page that says I'm totally trustworthy. And I totally didn't edit it myself, because I'm so trustworthy."