O.K., it's your worst nightmare, and you have to face it! You exchanged family tree information with a new acquaintance, both sets of data cover many of the same people, and you have some major disagreements! Your trees differ as to the parentage of your 5th great grandfather, your 7th great grandmother's maiden name, and the dates of birth of 12 scattered ancestors. Each of you started out believing your file contained only validated, trustworthy information.
Which of you will be the first to suggest the other has errors in his or her database? Who wants to become "the enemy" to be argued down, or straightened out, or ignored? How about it, hasn't this happened to you? Well, it will. Be patient.
You will sometimes run into people with absolutely closed minds, who will not consider, are not capable of considering for a second, the possibility that they could be wrong. If you have to deal with these people I hope you can find some other subject of mutual interest, because you are never going to be able to talk to them about genealogy.
Assuming you don't have the hopeless case above, one thing makes it possible to discuss those disagreements and keep the friendship. There is one simple fact that everyone who gets into genealogical research must accept, like it or not. If your family tree has at least four generations and more than one surname involved in it, THERE ARE ERRORS IN YOUR DATA! You know how the number of ancestors goes up exponentially as you go back farther and farther – two parents, four grandparents, eight great grandparents, 16 great, great grandparents, and so on. Well, the certainty that some of your information is in error goes up exponentially also. Some of your information came from the tightly stretched memory of your oldest relatives. Some came from old letters, old books, old guesses made by those who were interested in your family history before you came along. Some of the information represents rumor, maybe even gossip of the past. Some represents attempts by your predecessors to read hopelessly illegible handwriting or marks on tombstones. In short, guesses that became written down, hence obviously perfect. Repeat something long enough, and everyone will believe it. Publish it once and get the same result.
So both of you are now very fortunate, even though it may seem the opposite. You both have the opportunity to at best find and correct errors in your databases, and at worst identify linkages and dates that need further research for confirmation. What's so bad about those things? Why should anyone get bent out of shape over them? O.K., so in fact it is human nature to want to be right. It's hard for even scientists to admit it when they're wrong, but they have to, or they are only pretending to be scientists. Genealogical research is as much a science as any other, and those who perform it are scientists, whether they have a degree in the subject or not.
The two of you should be willing to investigate the discrepancies in your databases, not trying to prove you're right, but trying to find out what's true. The best approach would be to list all the discrepancies, then for each discrepancy list the evidence for each of the two current claims. If there is not enough evidence (probably the case), help each other plan how to try to get more evidence. Share each new piece of evidence with each other until one of the two claims has a clear preponderance of supporting data. To the extent and for the time in which you have not come to agreement, each of you should describe the two claims in each of your databases. It is important that the reader of your files be aware that there is an unsettled issue whenever that is the case.
If you need some help getting this research collaboration started tactfully, you might consider suggesting that your potential or actual friend read this article. That should be an adequate hint. You may discover a new aspect of this family tree searching stuff that is extremely rewarding! On the other hand, if you are one of those people who can't imagine you could be wrong, I'm going to ask you for a personal favor. Please don't start researching anyone in my family tree!!!!!