Let's say you had two iPhone 6s, and I asked to buy them both from you, but before I do that, I tell you that I want to see if the phones are in good condition first. So, you let me handle the phones.
Then, I "accidentally" bend one, and I "misplace" the other behind a bush or something so that it can't be "found."
The I tell you "OMG this is a huge accident I'm so sorry! But I don't have the money to pay for these phones I told you I wanted to buy. It's all a big mistake, and I can't pay... won't you please understand?"
Would you understand and walk away with no phones and no money?
You got me convinced and I trust you!