probably a scam.
Ways to avoid:
1. Ask questions, lots of them. Why did they buy it? Why are they selling it? Ask for a pic of a local newspaper taken with it? The last works well because you can look at EXIF data to see which camera it was taken with matches what is being sold.
2. If its a local store, ask if they got a warranty with their camera. Sale receipt? Warranty cards?
3. Ask if they have the box and accessories. If they don't have them or make weird excuses, either stolen or scam.
4. Offer to pay the asking amount paid for by check on a local bank, no Western Union, Paypal or wire transfer. Say you need it for a business expense/insurance purposes. If they decline, I have posted on CL details etc. The ad usually vanishes.
5. If they ask for cash, negotiate and state UP FRONT you will want to meet in a public place, you want to see a drivers license or other ID and you will bring someone along. I bring along two standard sales forms with room for : two names, an amount, a tile of the item in question, a serial number, a list any bits that go with it and room to write down their ID.