We've been in business for 20 years, and we've never had to offer a guarantee on this product, because as long as you don't add over 75ml of fluid, and make sure the temperature is correct when you hand over the sample, it's 100%. (well, unless a lab tech messes it up, but you just demand a retest in that case). What this means for you our customer is that the product works. There are, however, some limitations to using it.
You should not to use it for government jobs or government mandated testing, as that is a federal felony. (this includes truck / bus drivers, or anyone that works in a job that is government regulated like an airport or schools) This product should not be used for any medical health testing as the medical qualities have not been tested for.