If you feel like you need more facts or if you are acquiring a nanny without an agency, you can hire a detective service for as little as $30 (although it usually runs somewhere between $50 and $100—more if you want to cover multiple states) to run a background check that includes conviction records, DMV reports, ID and address history, and credit checks. Professional investigators can also find out whether or not a candidate really has a degree and from what school, perform a sex offender search, double check applications for omissions in employment history, determine how long someone has lived in your state, and get a complete list of past jobs and how long they were held.
While it may seem shady and a little exciting to hire a PI, it's something corporations do all the time before hiring employees for the mailroom, so it shouldn't be a big deal when you're hiring someone to care for your children. It's also completely legal and doesn't require the permission of the job applicant. However, in the spirit of open communication, it's a professional courtesy and the polite thing to do to inform all potential nannies that you plan to run a complete background check.
In fact, a person's response to this revelation is often telling. Someone who says, "Sure, no problem," is probably squeaky clean. Candidates who respond by admitting to a speeding ticket or a late credit card payment are also good bets. Everyone makes mistakes, but people who own up to them are a rare find. You want to hire a nanny who will tell you, "I'm so sorry, but I accidentally let the cat out and he's missing," or "I was taking Ryan to soccer practice and backed into another car in the parking lot," rather than one who'll pretend that nothing happened.
On the other hand, someone who honestly admits to drunk driving or check fraud should be graciously escorted from your home as quickly as possible. The same goes for someone who turns up with an abysmal credit rating. A little bad credit can be chalked up to immaturity or financial hard times. But major debt smacks of irresponsibility and only increases the temptation for someone to skim from the petty cash meant for the children's outings or steal your valuables a bit at a time.
While standard background checks are a great means to weed out the truly scary characters, they're still just facts on paper, and can even be misleading; a person can have a bad credit rating because of an ex-spouse, for instance. Personally spending time on the phone to check someone's references is the best way to really understand your best candidates. And speaking to former employers and friends can help tip the balance between two potential nannies that you can't seem to choose between.
Some nanny agencies provide the names and phone numbers of a few former employers, and some even include glowing testimonials from past families. Those are an excellent start, but a good reference checker is like Oprah Winfrey or Barbara Walters—someone who's bound and determined to get people to open up and tell you everything.