My wife is on a number of genetic genealogy Facebook groups, and this time of year is peak season for confused new posters who are desperately trying to get some rationalization as to why their father (or mother!) didn't match with them on 23andMe. Many just cannot accept reality and continue posting convoluted possible reasons ("23andMe messed up both me and my fathers tests, but we both still matched with lots of other people?"). It's quite sad at times
Why do you think the 23andme results can't be wrong?
Many years ago my father was once given hospital test results stating he was terminally ill with a heart condition. He knew he was somehow given a different patient's test result under his name when when his family doctor asked him if he exercises (he does) and the doctor said "That can't be your patient record. You wouldn't be able to exercise if your heart was as sick as the test result states." My father is still alive and exercising regularly today.
In a world which contains huge, systematic lab screw-ups (such as the FBI Crime Lab scandals), is there good reason to believe that 23andMe is particularly reliable and competent? Vs...one of our clients at $DayJob is a home mold inspection lab. Keeping their modest mold lab Officially Certified requires daily duplication, replication, etc. of dozens of individual test results, plus statistical analysis of those, plus...
Although getting serious statistics on the matter is not easy, the estimated numbers can be surprisingly high (e.g: "One in 25 fathers is not biological parent": https://www.theguardian.com/society/2005/aug/11/childrensser...)
If suddenly we discovered an easy way to give a hint you should do a DNA test, it could do some serious noise.