You can cross reference KBB, Nada Guides, and Black Book values to get a better picture.
Even then, sometimes those values are meaningless if no one wants to buy your vehicle.
I sold my 2012 Cruze last year, which booked in at nearly $8,000 between the different agencies. I had to sell it for $6500 because no one was interested at 7k or higher. I almost had to let it go to a lowballer for $6,000 but someone else came through for $6,500.
No one likes a Craigslist lowballer, and $16,000 -> $10,000 is a pretty darn strong lowball. That being said, there's no harm in sending an email and letting them know you're interested but can't afford their asking price. At worst, you're anonymously annoying someone you don't even know via the Craigslist mail relay.
I get very annoyed when I'm selling smaller items on Craigslist and I get low balled, but when I was selling my car it was not only validation that there are people who are actually interested in my car, but it also became a fallback - if the clock ran out I knew there was someone who wanted to buy it, even if less than I wanted out of it.
