Their data's accuracy is limited by the scope of their database. For example when running chimpanzee dna against a human database you find out their closest relatives are nigerian and/or black. From a traditional evolutionary standpoint this makes sense but any science can be perverted as truth and this scenario certainly just seems like fuel for racists.
In a case like Elizabeth Warren her DNA wasn't even compared to a sample of actual Native Americans making any results more or less useless and largely speculative.
When DNA is most effective is in direct comparison. These sites like 23 and me generally use different criteria (number of markers they use) and compare them to different databases of information. As far as rough estimates go it's not terrible but to claim it as definitive is a stretch at best.
do you even know how a genetic database works?
They get more accurate all the time but between one database and another you'll get a high variance in the accuracy of the ancestry data they pop out. W/ DNA as is used in court they're comparing a sample to it's closest match making familial identification have a high rate of success. The various ancestry sites use different criteria for the tests they perform as well. some look for fewer markers others look for more. Ancestral identification is only as accurate as the methodology and scope of the database used. You do realize there isn't a central one right?
what specifically is the fake part?
The over all concept?
or the genome statistics?