When putting your NFT for sale, it is delegated to an account owned by the marketplace program and added to a database which stores the data of the sale. When someone buys your NFT, the program transfers the SOL amount from the buyer to the seller, and then unlocks the NFT which is sent to the buyer. Releap uses both on-chain and off-chain data. The off-chain data is stored on a database and used to display all the NFT for sale on the main page, while the on-chain data is used when displaying NFT one by one, or from the ‘My NFTs for sale’ section in the ‘Wallet’ tab. On-chain data provides a secure and decentralized experience. In fact, the marketplace could be fully decentralized, but handling multiple thousands of NFTs for sale and displaying them with filters on the main page is currently not an option because of the request limitation on the Solana Network.