How to know who is talking to you on a spirit board?

I am a novelist, and also someone who wants to try using a spirit board. I am not on here for people to tell me that they're "evil", I don't believe it, so please don't. However, I do know that spirits will try to trick you, for one by saying that they are a spirit you have conversed with in the past. How can you be sure? Also, I would like to contact a relative of mine, how can I tell if they are indeed my ancestor or a spirit saying that they are? Maybe ask them a question that only my ancestor would know? Any other suggestions on how to properly use a spirit board would be appreciated. Thanks.