When selling anything you run the risk of timewasters. I've lost count of the number of time I've spent ages with folks, given them all the info and been as helpful as can be, only to never hear from them again (not so much with TAS and animals mind you) It's definately just part of it - unless you've agreed a sale and got a deposit there's not much you can do unfortunately.
But as others have said, there could be loads of reasons for someone not getting back in touch.