I ran into a guy like that before I hooked up with my current band - we got together and agreed which songs we were going to work on, I put in a load of time learning the songs then got an email from him saying he had "personal issues" and would have to hold off for a while. I had no problem with that, emailed him back saying to get in touch once he'd sorted everything out but then a few days later he posted another advert on JMB.
Just wish people had the balls to be honest with me rather than wasting my time...