How do you know your DNA test is accurate?

Another Good question, I've talked to 2 people in the last week about this.  They both found close DNA relatives, contacted them, and were asked, "How do you know your test is accurate? It could be wrong."

In 2012, a man got an Ancestry DNA test that turned out to be wrong.  Which was really awful for him, as he was an adoptee and the inaccurate test matched him to a "1st degree relative" (parent, full sibling, or child). Ancestry retested them at no charge, and they got accurate results: no relation.

To check your test's accuracy, ask a known relative to also get the test.  Use another DNA company if you want to get real nit-picky about it.  My brother and I got tested at Ancestry (at different times), we come up as siblings.  Our cousin Mike got tested at 23andMe, he sent his DNA results from there to GEDmatch: he is our cousin.

If you don't have a willing relative, you can get retested at another DNA company. Unfortunately this costs more money.