If you have saw an Ancestry commercial or are a member of the subscription site, chances are you have saw those small wiggling green leaves that indicate a potential match in the records to the person you're researching. Sometimes they can be helpful, but other times I think they aid in the proliferation of undocumented trees with erroneous genealogical information
About a year ago, my sister came to stay with me for a couple months. While she stayed, I shared my research with her and the genealogy bug bit her hard. She wanted to research the family tree too. I offered her my notebook, pointed her to some of the free websites, gave her some tips and sent her on her way with a caution to verify any information she used to build her tree, including any information she found in my notes.
A week or so later, she handed me my big genealogy notebook filled with family group sheets and informed me that I needed to update it because she had extended one of our family lines by several generations. I was excited because that particular line was one that I had been stuck on for a while.
She pulled up the tree she had started on Ancestry and sat back with a smug look. The first thing I noticed was that one person's residence suddenly changed from one side of the country to the complete other end. I was curious about this because as far as I knew, the family had always stayed in one particular region. Perhaps I had been looking in the wrong location all this time.
A little more digging and I saw the problem. She had got her information on the move from an unsourced family tree. Apparently the original person couldn't find this individual in the location they had lived previously so they expanded their search to the entire country and jumped on the first likely person. The only problem was while this person had the right name and only a little off from the age of our person, none of the other information matched. A few more minutes of researching verified that this wasn't the current individual.
When you encounter a list of hints at Ancestry, there's a link that says learn more about Ancestry hints. The first thing you see on the page that loads is "Ancestry Hints give you helpful, accurate leads to your next big discoveries in family story." Someone seeing that would be led to believe that a wiggling leaf means the record is a definite match.
A little further down the page, there are clues that the hints might not be accurate: "hints link you to historical records and trees that might hold answers about your ancestors.", "abbreviated list of possible record matches for a given ancestor", "Before you add a record, double-check to make sure it describes your ancestor." (bold emphasis is mine)
For those new to genealogy, like my sister, these leaves can result in missing one of the most important parts of genealogical research, applying the Genealogical Proof Standard.
A reasonably exhaustive search
By relying on the leaves, you may not be searching all available records. The reliance of online records alone is not a reasonably exhaustive search.
Complete and accurate citation of sources
Using someone else's family tree is always dangerous. Even if the tree is documented, it is important to double-check all the sources used to build the tree. One minor error in interpretation of a record can skew the entire tree. Without evidence of the individual moving cross country aside from a census record of a person with the correct name but not other matching details, it's hard to rely on the information.
Analysis and correlation of the collected information
Had my sister analyzed the information found as a result of the tree she used, she would have realized that not everything added up. The age was slightly off and the birthplace of the individual and his parents were different from all other records found.
Resolution of conflicting evidence
Conflicting evidence doesn't necessarily mean you're not dealing with the same person. I've came across several individuals in my tree that had differing information from record to record. I've came across people that aged little, if at all, between census; people that said they were older to get married or join the military; and, on my husband's side, a family that came from a different country on every census.
However, these people all had reasonable reasons behind the differences and their core details didn't change much. They still had the same families and lived in or near the same locations. The family on my husband's side had a credible reason for a different country every census. The country they came from was dissolved and divided into multiple countries, which sometimes changed names.
Soundly reasoned, coherently written conclusion
Without good reasons behind the various discrepancies, you can't come to a credible conclusion. This throws doubt on your entire research.