Also got a text just hours after listing my car on cars.com.  "Is your listed ad on cars.com still available?"
sounded suspicious, and after reading the other comments it looks like it definitely is!

I recvd a text from the same number after posting a car for sell on Cars.com.  They sent me an email address. I responded.  They wanted to buy my car for the total asking price.  Then mentioned they would have the car picked up as it was going to be shipped to China.  I told them I preferred cash as I preferred to deal with someone local.  No additional responses.  This is Def. a scam.  Be ware!!

Got a suspicious text message right after posting a car for sale on Cars.com