Check, check and check again
Online genealogical data-bases such as Ancestry and FamilySearch have been a boon for family historians. You can now search through parish, census, and BMD records from across the globe. As good as their original sources are, these sites also encourage family historians to share their own research and genealogies on-line. Those who do so, are providing free data to whomever uses the sites.
By all means check these personally complied genealogies and family histories, many are done very well, but ensure that they are properly referenced before you decide to include them in your own family history, and always check that they make sense. Once an error is in the system it can be replicated time and again.
It is not only on-line resources that should be checked. I have found errors concerning my family in well researched, published biographical indexes, and these errors have been repeated in other people’s personal genealogies.
If a source lists a birth date, a parent’s name and location for example, you may think you are there. But if you can, find the state registration for the birth to double check. Getting hold of the original birth certificate can be a revelation, and can provide new leads, such as mother’s maiden name, and the age and occupations of parents. Check as many records as you can for each individual to ensure names, dates and locations match, or make sense?