an independent laboratory testing for Henna

Hi,

   http://www.mehandi.com/ often claim their products of Henna were tested by  an independent laboratory with any reason (such as finding adulterants, lawsone percentage etc.) that is the good method. However how can I know the products that I buy from mehandi.com are really tested  ? Are there the back tracking processes for customers ? I ask this issue because I want to show my cutomers for the authenticity / reliability

Thanks,