I get most of my epubs from Kobo. I never use the kepubs and only ever download into ADE and then Calibre.
In almost 2 years I have only had one book which had major problems. I notified Kobo hoping they could replace it with a "corrected" book but they offered me a refund instead. As I was able to fix the worst of the problems in Calibre I opted to keep the book and didn't bother with the refund.