This is really unfortunate. In past community science projects, we've fundraised to be able to pay for some samples (chosen at random) to be tested at an accredited lab, then compared those results with ours to get a correlation curve to verify accuracy and the % similarity. Another good option is to partner with an academic research institution on the project. Publications are currency in academia, so if they can get a paper out of it, it will lend much credibility to your results. At my school, UCR, we have a health disparities research institute which works with the medical school and my lab in Enviro Science and Tox on community-academic research partnerships which are founded on good values and collaboration. Let me know if you'd like me to connect you or if there are other ways I can help.