Shoes for sale

Everything worn by human beings gets sold on the streets of Phnom Penh, from hair ribbons and hats to used shoes. There is quite a market in used shoes here. This wagon pulled by a motorcycle has quite an impressive assortment. For me the shoe wagon raises two questions: [1] How do you shop for shoes when the wagon comes around? Do you pick a style (boots or sport shoes or hard soles) and then sort through that category looking for the right size?, and, [2] How does a market for used shoes exist? I tend to wear my shoes till they are not good for me or anyone else.