My daughter gave up trying to sell clothes on ebay for exactly the same reason and now just gives them to Sue Ryder's Charity.
I'm afraid I confirm that a minority do abuse the mail order business.
When Next Directory first started I was their local courier. At the time they used to sell dinner suits. When I delivered the suits customers would often arrange for me to call back on the following Monday to collect the suit after they had worn it for the occasion.
At about the same time I sub-contracted to another courier distribution company and collected all their returns in a given area.
Always remember a request I got on Christmas eve to collect a large parcel.
When I went round to get it the lady said she hadn't packed it yet .." not to worry I said, I have got loads of packing materials and I will help you do it ".
Sheepishly she asked if I could come back after Christmas ... otherwise the kids wouldn't have a Christmas tree.
Needless to say I demanded the tree there and then, otherwise I wouldn't get paid. I left the kids with no tree and in floods of tears !
Only joking ... I left them with it and I called back in the New Year... got a box of shortbread into the bargain !