we have 3 people tested at ancestry, with 2 more test kits in hand. we have 5 tests at 23&me with 3 more in hand.
here, all 3 tests came back exactly as they should have. my granddaughter tested as 2nd cousin to my nephew and both tested as 4th or 5th cousin to my 3rd cousin.
same results at 23&me, 1st cousins tested as 1st cousin and both tested as 3rd cousins to the 3rd cousin. all dna tested exactly as paper trail predicted.
i have talked to one active genealogist who has 20+ family members tested, all test exactly to each other as predicted. be assured the tests work right.
that said, people and machines do make mistakes, but the theory and testing practices of dna work as advertised.