I need to know before a purchase whatever site I'm buying from. Who knows I may end up with a PDF ebook
On fnac.com, the affiliate seller of Kobo in France, when buying one can see the format and the DRM status but not the devices on which said ebook can be read. One day when I wasn't really careful I bought a guide book which is full of pictures and weights a little less than 80M

It was an epub file, so what can go wrong I was thinking. Well tablets can deal very well with epub files too and I did forget that (at that time).
So now what I want to see before a purchase is the format, the DRM status and the devices that can be used.