Hello, I have checked the links here:
http://rachelandrew.github.io/eu-vat/third-parties.html

(anyway thank you very much for the list)

and saw on some services that they only intermediate the business between customer and seller (e.g. only safe download of the file) but the business happens between customer and seller so in fact this does not help in this situation 🙁

So maybe there needs to be some kind of information that the one who wants to sell the downloadable file will be in no connection with the customer but only with the services which provides the download ???