Re: Two questions
Have never returned an ebook and only one paper book (returned it the next day when I realized I already owned it - yes, oblivious IS my middle name, how did you guess?).
I get so many different recs from so many different places, I couldn't give you a trend. However, my current favorite place is on Goodreads. Since I know my friends' reading habits - what they like and not via Goodreads, when they put up a new book they are interested in, I might just check it out. In those cases, the covers don't make a difference.
However, when I check out the 'people also bought' lines under books I'm interested in, the covers ARE important in drawing my eye to a book. The the title. Then the heft of stars (though I also often ignore those and just head directly to the reviews themselves) and then if I'm interested, I'll check out the reviews.
Does that help?