In addition to what everyone else wrote, note that your proposal is enormously economically inefficient. The businesses that sell microwaves are much better pos

In addition to what everyone else wrote, note that your proposal is enormously economically inefficient. The businesses that sell microwaves are much better positioned to... well, sell microwaves... than the average consumer. They are the least-cost avoider of the social harm of things going to waste (which is what happens when unwanted item X doesn't get bought off Facebook Marketplace or Craigslist or whatever and the original purchaser finally tosses it). If items are going to go unused, it makes economic sense for them to be sold on the secondary market. If they are going to be sold, it makes economic sense that they be sold by an entity that is good at selling them. The original merchant has a significant comparative advantage in selling items it already sells compared to any given consumer.