6341995:The candidate gave us a former manager. The manager ddin't speak badly of the candidate, but not glowingly either. At the end of the conversation it was determined that there were more warning signs. How can that be communicated back to the candidate?
This is one of those times where you have to ask yourself whether or not the reference is helping you understand anything. Most business managers don't know much about references other than that you can get sued for giving one. If the manager is being guarded and doesn't really say anything, that MAY be because he speaks the language and understands that a nothing special reference is the same as a bad one, or it may be because he doesn't feel free to speak, even about positive stuff. If you've thought about that kind of thing and your gut says this guy was giving out the "stay away" signals regarding your candidate then you have to go with that. Just understand it's not the same as a negative reference or actual evidence of fitness for duty.
If you plan not to hire this person because of a single reference, despite the fact that the reference never said anything bad about your candidate, then you are kind of in a pickle. The real reason is that you have a hunch. Now, you've said that there were more warning signs. Those could be much more dispositive than your hunch based on a mildly positive or neutral reference. All you have right now is that "the outcome of your reference check did not meet expectations." This may get you into the middle of a slander case, of course, because the next question the person will have is "what didn't add up for you?" You, of course, will not want to point fingers, and if there's enough money on the table, or the candidate is bored and wealthy, they'll force it out of you through the subpoena process. The short version of this story is that I really like to minimize the impact of references on hiring decisions when I use them at all.
Alternatively, you can dodge the issue and say something like, "we've decided to continue our search. While it's true that you aren't a bad fit, we're really looking for someone who has more <insert candidate's weakness here>". I'm really interested in the totality of "warning signs" you have because you'd really rather give reasons other than "because someone didn't speak well enough about you behind your back." In the end, you plan to continue searching. Have you made a job offer yet?