As a reader who gets the vast majority of her fiction reading material from Kobo, I put a lot of weight on the cover when I'm looking at books whose authors are new to me. Amateur covers -- hand drawings from someone who's about as artistic as me, illegible fonts, clumsy kerning, zillions of competing images, etc -- are an immediate no. Since Kobo shows a title and book cover and the first ~30 words of the blurb, and from there you click to read the full blurb, the cover plays a large role in whether I click. In the romance genre, I use the person(s) featured on the cover to tell me the age, gender, race, and species (for paranormals) of the protagonist, as well as the setting. I use the style of the cover pose to tell me the heat level, tone, and more about the setting.
I am vastly more likely to buy a book if I've already read a book by that author. I quite often buy 'the next X books in the series' if I've downloaded the first book for free and loved it.
That's just one datum point, but I'm probably not alone in my shopping habits.