Buying an iPhone 5S off of Craigslist?

So I'm buying TWO iPhone 5S's for $750. The seller wants it in Cash. They're willing to meet up in a public place. The phones are supposedly "Factory Unlocked". I asked why they were selling them and they said that they bought and resold phones.

Is there anything I can do to make sure that the phones do NOT get reported as Stolen/Lost after purchasing them?

I remember reading something about if they're factory unlocked, I could call apple and have the ownership transferred to me? If that's possible.

Should I go on with the purchase or should I just back out?

Added (1). The phones are still in the box and with wrapping on it. So they're not stolen. They're willing to let me check the status of activation when I meet them, but they won't send me the IMEI number through text.

How do you know they are not stolen? You will not be able to activate them if they are and you may be charged with receiving stolen mdse

I wouldn't buy them on Craigslist, I don't know if you heard an incidence where a girl in Australia bought two iPhones online and instead got two actual apples.

http://www.huffingtonpost.com/2013/08/03/iphones-apples-_n_3697669.html

2 factory unlocked iPhone 5S for $750 is too good to be true deal when one factory unlocked iPhone 5S costs $650. I would refrain from buying from them. They can be in box but they can still be stolen from warehouse or shops and once you activate the phone, you'll be in trouble in couple of hours or so. So think twice before buying from Craigslist. I would suggest you to pay with PayPal, you can at least file a claim if anything happens. If you need factory unlocked iPhone 5S at reasonable price and pay with PayPal securely, mail me.