How to sell a new found iPhone?

Okay so i was walking my dog and I stumbled upon an iPhone 5s in an otter box case, and I was gonna call someone off the phone to return it, but it hadn't even been set up yet. The phone was still brand new like when you first buy it. I want to keep it now and sell it, but how would I do this? What if it's reported stolen? What should I do if it is stolen? Or is this whole thing just too good to be true?

You have a legal obligation to report the found item to the police. If it goes 30 days without being claimed, it's yours.

Turn it in to the police or put it in the Lost and Found section of Craigslist or other site.

Finding lost article that's not yours--not a crime.
Keeping lost article that's not yours--a crime, called theft
Selling stolen article--an even bigger crime, could be misdemeanor or felony

Sell it on-line… Craigslist.

Find an Apple store and have them help you find the owner. But, then again, it doesn't sound if you really WANT it to go to the rightful owner, and are just trying to make a quick buck off someone else's loss!