First, a cautionary tale.
In our previous family business, we hired a high-level marketing manager who was a dream on paper. We'd known him for years. Spent his entire career in the industry, worked for a high-profile major player, everyone knew and liked him. He was bright and articulate -- the whole package. But he lived out of town and his spouse had an irreplaceable job, so we were even more careful about the hiring decision than usual. We wanted to be sure we left no stone unturned and nothing to chance before relocating him and his wife.
Everything looked good, we hired him-- and then he showed up for work.
On the morning of his first day, I went to his office and found him lying on the floor with the lights out. I thought he was dead. When I turned on the lights, he popped up and told me that it was one of the ways he does his thinking. I told him that, aside from the fact that he didn't yet have anything to think about, his "technique" might not go over well in our office environment. He understood, so the next day he changed his thinking method to standing flat against the wall in the hallway with his eyes closed, listening to classical music.
It went on and on from there. He made obtuse comments and weird suggestions in meetings, and didn't seem to grasp anything about what we did. It was as if we had hired one guy and his evil twin subbed in for him; we had no idea how we could have been so far off in our assessment, especially with our excellent hiring track record.
We honestly never figured out what more we possibly could have done before hiring him that would have given us any clue. But fortunately, we did put in a safety valve: We had asked him to come to work on a commitment-free trial basis before relocating permanently. So it was (reasonably) painless when we told him it just wasn't a fit. It could have ended much worse.
So, what can you do to make sure the person you hire is as close as possible to the person you interviewed?
DON'T be an interview robot. I know there is a ton of science behind structured interview processes, and they may work for some (typically large) companies. But I hate 'em. I am hiring a person, not a question-answerer (I aced standardized tests in school, but was not a great student -- it's not dissimilar).
So, once I get past assessing specific qualifications and work history, I prefer to spend most of the time having an open, friendly conversation; it tells me so much more than "tell me about a time you solved a problem--" This is especially true in very culture-centric companies like ours. Bring it on, HR professionals, I'm ready.
DON'T make major difficult-to-reverse decisions prematurely. Even if you've done everything possible to make a good decision, and even if you are in an employment at-will state, make provisions for possible surprises. Probationary periods are common and wise, and if you offer employment contracts, make sure they include such a trial period and that the employee understands it is in his interest too. Don't relocate anyone until you're as sure as you can be. And of course, document everything.
DO get "real" references and check them. Even the most honest rÃ©sumÃ© is an advertisement. The best interview is still a sales pitch. So third-party information is critical to building a complete picture. Most candidates will provide only positive, cooperative references, and past employers -- especially large corporations -- will often give nothing beyond employment confirmation. But most of the time one or two references will (intentionally or otherwise) give you "between the lines" information if you listen carefully. This can be the most critical information of all.
DO check a candidate's online image: This has been much-discussed and at times controversial, but searching for online information about a prospective employee is a prudent and often very telling tool for getting to know the real person. Rest assured that a thorough candidate will dig up anything he can on you and your company too, as she should.
By doing everything you can to get to know the person you're hiring -- well beyond the skill set or job history -- you'll reduce the chances that "someone different" will walk in Monday morning.