First, what exactly is backdoor referencing? Some people call it a backchannel reference, or do this as part of a comprehensive background check. We already know that references provided by candidates tend to be skewed positive, and that’s not always helpful in deciding if a candidate is the right fit.
So how do you get a more balanced picture of what this person is actually like in the workplace? Scour your company network (both internal and external) for other people who have worked with this person, then reach out to these people and see what they have to say. Chances are, you’ll get a broader range of feedback. This feedback can be helpful to gain more context about the candidate but also help you to speed up your hiring process. Think of backchannel references as a gut check, it should be a quick thumbs up or thumbs down to help you decide whether to prioritize a candidate in the process.
Is it legal? Yes, IF you do it right. (standard disclaimer - consult your lawyer etc). Is it ethical? Depends who you ask. If you want to stay out of trouble, there are a few things you should consider before hopping on LinkedIn to reach out to your network.
You need written consent to perform any type of reference check, backchannel or otherwise. That being said, if the candidate confirms that you’re allowed to check their references, you are within your rights to do so through any method you want to. The only exception would be if the candidate specifically states that they don’t want you to use any sources other than the ones they’ve provided to you. A good way to cover your bases is to simply ask the candidate "Is it ok with you if we ask mutual connections in our network about you? We promise we'll do it without alerting your current employer."
You might be putting the candidate’s current job at risk. If you’re not careful, there’s a chance that your clandestine reference checking will tip off the candidate’s current employer that they’re on the hunt for a new job. If that happens, you could end up damaging their professional relationships, or even getting them fired.
You might be getting a one-sided account. Typically, people will provide a candid backchannel reference only if they’re promised that it will stay anonymous and confidential. This means that you might not be able to get all sides of the story since the conversation “never happened”.
The point of seeking out other references about a candidate is to help you gather qualitative feedback to speed up your hiring process and make better hires. That being said, conducting a rigorous back door reference process can be quite cumbersome and the work might always be worth the reward. Here are a couple ways to think about backcdoor references to avoid reference hunting burn out: