Probably most of you already know about this, but in case it helps someone I wanted to bring it to your attention. My wife posted a car for sale on Craigslist, and within minutes she had 5-10 texts.
What they do is say that they have cash in hand and are willing to buy the car, but they want you to run a specific background check on it. The check can be $30-$60 dollars depending on the site.
They are the ones running the background check sites. Just giving a heads-up. I did a little research and it's a well known scam.
If you are selling and you come across one of these guys, don't fall for it.