Keep it on the back burner…without forgetting it!
You have a nice problem on your hands. Out of your three final candidates, your client does not 
know which one to choose (and yes, it does happen…). He decides to pursue the first one anyway but asks you to “keep the other two on the back burner” just in case…
What do you do, and above all how do you do it?
1 – Try to understand your client’s motives. Why the first and not the second? What pushed them towards the first candidate and are they sure of their choice? On the same note, are they happy enough with the second candidate in spite of them not being first choice (it could avoid resuming recruitment in the next six months to the benefit of both the client and the candidate).
2 – Accompany your client and follow the process so that their decision is made within reasonable time-limits. Ideally, you must not stretch the process out for longer than two weeks, as beyond that you will lose the ‘momentum’ of the candidates and their interest will decrease. You can no longer guarantee your client that they will still be interested.
3 – Inform the candidates of the process. You can mention to them that there are two or three final candidates and that it’s a close call. You can talk to them about their strengths and weaknesses. Avoid telling number 2 that he is second on the list; no-one likes to learn that they are plan B.
4 – Don’t leave them without news! Even if you have nothing more to tell them, a simple phone call to let them know that the process is running it’s course and you have not forgotten them will do. Keeping in contact allows you to have better control of the situation.
5 – Don’t forget that as long as nothing is signed, nothing is complete! There are always surprises. If you have kept in good contact with the candidates, if you are certain that they understand the basis of your decision and thoughts, it will be much easier to deal with their expectations…and their impatience!