I remember one visit to an op shop in Sydney - the one that locals called "Sally's,'" short for Salvation Army:

For my flight from Sydney to San Francisco, a friend who used to work for an airline purchased a companion ticket for me. The ticket came not only with a really good discount, but with a dress code requirement that included no jeans and a need for shoes that were much nicer than the ones I had with me.

I have no problems buying used clothing, but I had never worn used shoes. I needed a pair. I got one at Sally's, just to wear in the airport and onto the plane.