Yes, 2. The first was because I decided a flap style wasn't really my style. The second because I found I wasn't using the bag; the tag was still on six months later. I finally decided to return it which helped defray the cost of a tote I was dying to buy.
Yes. In one case, the bag was simply too difficult to get my things in and out of; I didn't make it out of the bedroom! The other 2 times it was due to sight unseen: the color was NOT going to work w/my wardrobe or me.
It happens. However, I have always found a bag to purchase when I've gone to return, so I don't think the SA was too upset, lol.