eBay is one of the largest online marketplaces that exists.
It facilitates the buying and selling of new and used goods between people across all continents and countries around the world. It is used by established businesses, manufacturers and individuals; essentially anyone can sign up for an account. Goods can be sold by auction (with the option to put a minimum reserve) or by fixed price.
The interaction between a buyer and a seller is recorded by a feedback system. Each reviews the transaction quality and efficiency, and rates based on this [both a written and star system]. If a user receives three strikes [from failing to pay etc.] their account is voided.
eBay is linked to PayPal [they are the same company] so payment is incredibly secure and fraud-free. However there are often other payment options available; bank deposit or cash on pick up, depending if the item can be posted or not. Postage rates are determined by the seller [either courier rates or Australia Post].