The way people behave when they leave their current job to come and work for you is a critical piece of information that can be very valuable. One of the very best open ended interviewing questions that you can ask is how much notice the applicant has to give their employer before they can start their employment with you.
If you play your hand right, they have no idea how quickly you want them to start, and their response to the question regarding their notice period may reveal some very interesting information. The key thing here is that it is a great opportunity to get beneath the surface and identify what kind of person you are really dealing with.
I have had responses to this question that are all over the map. Some people say "I have to give two weeks’ notice but I really want to give more because I don't want to leave them in a hole". Others say "I can start as soon as you like because I don't have a contract and they can't hold me to any kind of terms".
The person giving the latter response has just given you an interesting insight into their personality. While it may be that their current employer has lost any rights to their loyalty, it sends a message that you should really heed.
Then you can start to push and really learn more. The mistake that so many people make is that they are in a hurry to hire (which is always something that should be avoided) and they push the new hire to start more quickly than they would ideally want. The employer is too often blinded by the need to hire and fails to recognize that the decision that the new employee makes is a litmus test regarding their personal values.
Remember this. The probability is that when the time comes to leave you then they will behave in exactly the same way, and if they left their last employer in the lurch, then they will probably do the same to you. Because of this, I have routinely eliminated people that I really liked from consideration because they were prepared to leave their current employer in the lurch. I simply didn't care for the ethics that they demonstrated.
One interesting deviation from this was a woman that I wanted to hire who told me that she had sued the last two employers for breach of contract. On the face of it, this is not somebody that you want (and the peer group that I was in at the time advised me against hiring her) but I delved a little deeper, and found that she really had a good case against the people she worked for previously who really were behaving poorly. I hired her, and she was a great employee..... as long as I lived up to the commitments that I had made to her. She never sued me, but she did sue the next person that she worked for!
Over the years, I have had some dramatic leaving stories, and I wonder exactly what they told the next employer. Very few of those employers called me to ask for a reference, but if they had I would have told them the circumstances under which the people left.
The irony in all this is that even if they had called me and even if I had told them what I thought, it would probably have made no difference whatsoever. They probably would have gone ahead and hired the person and completely overlooked the warning that was inherent in their behavior when they left me to pursue their shiny new opportunity.
Some of the more dramatic leaving stories can be found in the "employee behaviors" section on the website.