It makes my skin crawl actually, the thought that "certain" items could have been used by someone else. I have no objections to people receiving goods, for instance, a bracelet, and not liking it and sending it back. Clothing however should only be sent back if it has not been "worn" to go out to something. Tried on in front of the mirror is one thing but wearing something to go out in for instance to an occasion and then sending it back is just unacceptable and anyone who does this should look to the way they have been brought up.
How anyone could have the nerve to be such a cheapskate I do not know. As for people who would use bedding for nearly a month and then re-package it and sent it back, well they are just the lowest of the low.
There are some dirty b*eggars about!
As for hight street shops. It has always been my belief that stores such as M & S keep their returns to one side until sale time and then put them on a dedicated "sale" rack so that anyone who buys from the "sale" rack at least buys things sold as seen and with the understanding that they are taking pot luck.