How to tell if a iPhone 5 has been opened?

So I'm thinking of selling my iPhone 4S and buying a iPhone 5 off of either craigslist or ebay. My worries is that I buy a iPhone 5 and it had been opened before and tampered with. I was wondering if there's anyway of being able to tell if a iPhone 5 has been opened up before.

Why don't you just google it

If the seal is broken

Usually phones that are listed as "new" on eBay are new. Also if you can't tell that it has been opened, does it really matter? Though when you get the phone, you can go online to the Apple website and enter the IMEI number here and it will tell you its warrenty expiration date which will be 1 year since its first activation, you can determine it from that. Best answer please, hope this helps you!