If you have agreed on a price with someone but they haven't communicated back about test driving car and someone else wants to come test drive--is this ok?

It just happened to me. "cordell" offered to buy my car. i accepted. Cordell was to set up a time for a test run. Three days went by, so I wrote back saying, "Cordell, this deal is dead. I am showing the car to anyone else who wants to buy the car." Car Gurus should give BUYERS 24 hours to respond or the deal dies. John Tyler - monroe, NC