You wont get a guarantee ever so foget about that, you are over thinking and wasting your time. As I said when it comes to herbal supplements or anything thats not strictly regulated you will always have an element of risk and if you cant accept that you need to stop consuming. Most people in europe who smoke weed have no idea of its growing condition or contamination but its just tough sh*t unless its legalised and regulated. In thailand where its grown, legal and sold its consumed by thousan