If your ancestor has a boarder, hired man, or anyone else living in the household who is not a member of the immediate family, have you researched that person thoroughly? They may be related to the family even if the relationship is not specifically stated.
My ancestor Barbara Haase and her husband Conrad have a fellow German living with them in the 1860 census. I discovered this years ago and really had not thought about it since. I now know Barbara's maiden name which is somewhat close to the last name of this unknown individual living with them in 1860.
Researching this man further may be worth my time. He may be totally unrelated to Barbara and Conrad or there may be a connection.