Gondola shelving is stronger and more versatile than most styles of retail store shelving. It is durable, often outlasting the life of the retail business it services.
Gondola's durability lasts long into the secondhand market, and can outfit several stores during it's lifespan.
Many major brands, like Lozier or Madix, have 20 year old parts that can often be integrated into shelving that is manufactured today.
This long life, backward compatibility and current availability of parts make buying used product a good way to save money, and allows some dealers to sustain used product year-round.
Many closing retailers, especially chains and larger stores, will go through some form of store fixture liquidation process. Used retail shelving, in one form or another, is the backbone of the store fixture liquidation business.
Used shelving gets around, and used shelving is around.