What can you buy at the Agora?

Could you elaborate on the variety of items available for purchase at the Agora? Are there any specific types of goods or services that stand out as particularly popular or unique to the marketplace? Do they offer a wide range of products, from digital goods to physical items, or does their selection focus more narrowly on a certain category? Additionally, is there a system in place for ensuring the authenticity and quality of the goods being sold?