Unfortunately, they mention no sources. The vials on the pictures in the PDF also do not have any labels, except for one shop. Shop "C" looks a lot like the vials offered by
https://www.facebook.com/tan.labs. Could also be they just stole that picture, but Google turned nothing up.
That's the question. I'm sure many are ordering from sellers in China, for example Alibaba ones, but I read in a few forums that there tend to be lots of scammers and people selling products without proper quality control.