TWICE A YEAR, Graanmarkt 13, a concept store and restaurant in Antwerp, Belgium, reaches out to clients, but not to promote a new collection or a final-markdown sale. Instead, it asks customers to bring in old clothes, which the whole store then turns over to sell. Participants get a voucher to put toward new items.
It’s just one of the radical ideas from Ilse Cornelissens and Tim Van Geloven, both 39, the married couple who started the place. Sustainability is a common word these days, but they take it to new extremes at…