I had that same experience when I tried to sell my wife's car. The exchange went like this:

Them: "Hey, I saw your car for sale. I always run a check on the VIN before I sell a car. You should really try XXXXX.com, it's half the price of Carfax! Here is the link: "

My reply was this: If you want to run the VIN, I'll send it to you, knock yourself out.


Never heard back from him.