Buying in Craigslist is perfectly fine as long as you filter out the scammers by looking at the listing, their responses etc. Finally tell them you will meet in a carrier store so that you can verify that phone is paid off its a carrier branded phone. If it's unlocked non carrier phone, I would meet in a public place like Starbucks, ask for proof of purchase if possible etc. Also, meet in a location you are familiar and comfortable with.