Not so long ago I was conducting research on my husband's side of the family. After speaking to my mother-in-law (MIL) whom I adore, I decided to try and flesh out details about her father. He had passed away some years earlier. It didn't take long to find him. I found him listed on a death index, a record of his divorce from my MIL's mother, but I also found a record of another marriage.
This made me sit back and pause. MIL hadn't mentioned this. Did she know? Was she supposed to know? Did she want anybody else to know? Would this be a traumatic revelation? What to do? After a day of pondering these questions I called her. We exchanged the usual banter and finally I asked if she knew anything about her dad getting remarried to a woman named____? The second of silence was followed by a big intake of breath and the exclamation of, "He told us he got remarried, but we didn't believe him!"
Conducting interviews are great, and they give you details that you might not otherwise find. We are usually cautioned that memories are faulty or details may be embellished over time. In other words, find supporting evidence!
I never considered that my source wouldn't believe information told to her by a primary participant--her father. Mostly I'm relieved this wasn't an awful revelation, and we've all gotten a good chuckle out of it. For me it was a good lesson in source reliability.