no due to them being worn by someone else who stands differently and wlaks differently - this makes them unsuitable as a buy on my feet which I want to be nice and comfortable and not slip in the wrong places as they are worn awkwardly
Yes, usually "worn once" or so . I have lots of nice shoes that fit me that obviously didn't fit someone else. They include some Gudrun Sjoden red shoes (£10, £89 new) and some navy Unisa Heels ( £5, £105 new) I wouldn't buy anything that was well worn but there are some real bargains to be had.
Yes I would buy and also sell them! Well not so much selling anymore as I have got rid of all the don't quite fit/not comfortable/too high shoes that I did have. I wouldn't buy or sell shoes on ebay that have been worn as such - they have to be pretty immaculate. Basically the mistakes/the not good fit/ the too-many-shoes clear out.
Thing is, with shoes someone else has thrown out - there was a reason. Yes, I buy second hand shoes from charity shops. But sometimes I've had to pass them on again, because I find they rub in the same place (probably) as they did on the person who handed them in in the first place. But no harm really - charity shop shoes are usually no more than about £4, and £4 is quite a good donation for the charity, look at it that way. As for posh brands from eBay - well, if they don't fit comfortably, you can relist and resell them yourself. I wouldn't buy shoes which look well worn, only almost as new.