Jr.s and Sr.s
If you're looking in the census, and you come across a John Smith, Sr., on one page and John Smith, Jr., on another page, don't assume that they are father and son. He may be a nephew. The same thing happens when speaking of a family member. He/She may have called a family friend "Aunt" or "Uncle", but they might not have been family at all. Growing up, in my community, we were told as children, to say "Aunt" or "Uncle" as a form of respect. I referred to a family member as "Uncle Anthony" when I was growing up. It was only as I started genealogy research that I thought to question whether he was my father's or mother's brother. It turned out that he was not either one's but rather was my father's uncle, brother to my grandfather.