Sorry, now I understand the question correctly. The Tolino is "free". No bookstore is preset.

As long as the bookseller is a distribution partner of Tolino Media, you are free to choose your bookseller. In other words, you can choose one from a specific list. (Google: Tolino Booksellers Switzerland)
EPUBs and pdfs can also be transferred via the computer/TolinoCloud. That's why it's not so critical which bookseller you choose.
If you choose OrellFüssli, you can also buy / download EPUBs from exlibris / load them onto your Tolino via the cloud.