If It Happens, Shame On You !
1. Your candidate accepts an offer with another company. And you're totally surprised.
2. Your candidate accepts a counter-offer from his current employer.
3. You client makes a good offer and your candidate says she needs to think about it.
If these things happen, you didn't ask the right questions in advance.
via Jason at Recruiting.com
Comment: I don't know how you stop a candidate from accepting a counter-offer. Or from deciding to sleep on an offer even if she's told you she's ready take anything that meets her alleged requirements. She might not even tell you that she is interviewing with another company (tho they usually do if you ask).