The other method is to simply search for products, and then look for “More Buying Choices” underneath an item. There’ll be a link that shows how many “Used & New Offers” are available.
You’ll find the same thing at the bottom of the “About This Item” section on a product’s page.
This takes you to a list of all available products in various conditions. Be sure to note the “Sold by” and “Shipped by” labels here. Read the condition descriptions and check the seller ratings before you purchase a used product.