On-line trading services in which seller posts products to be auctioned and bidding is done via the Internet; Operating on-line marketplaces for sellers and buyers of goods and/or services; Providing a web site featuring consumer information on various publications and providing hyperlinks to on-line retailers that sell the publications; Providing an on-line searchable database featuring used books being offered for sale and buyer/seller contact information; Providing an online marketplace for buyers and sellers of goods authenticated by non-fungible tokens (NFTs); Provision of an on-line marketplace for buyers and sellers of goods and services; Provision of an online marketplace for buyers and sellers of downloadable digital art images authenticated by non-fungible tokens (NFTs); Provision of an online marketplace for buyers and sellers of downloadable image files authenticated by non-fungible tokens (NFTs); Provision of an online marketplace for buyers and sellers of downloadable music files authenticated by non-fungible tokens (NFTs); Provision of an online marketplace for buyers and sellers of downloadable video files authenticated by non-fungible tokens (NFTs); Provision of an online marketplace for buyers and sellers of goods and services; Provision of an online marketplace, using blockchain technology, for buyers and sellers of downloadable digital art images authenticated by non-fungible tokens (NFTs)