I've sold 5 or 6 cars myself. It's not hard to sell an expensive car but it does take time. You have to be available for people to come see it and test drive it. Some people may want to take it to a mechanic for inspection. It is a fair request.
In my view, the biggest issue these days is payment. Whether they are paying cash or financing, their bank will give them a certified check. It is not hard to print a fake certified check. There are a few things you can do to protect against this.
1. Take a picture of their driver's license before the test drive.
2. Don't sell it if you think they are shady.
3. Make the transaction during bank hours. Call the bank to verify the check.
Here's a decent article from Edmunds:
http://www.edmunds.com/sell-car/edmundscoms-quick-guide-to-selling-your-car.html