Arbitrage, or true arbitrage, involves buying and selling a security and taking advantage of prices differences that may exists on different markets. While rare, this does happen from time to time. For example, suppose you find on eBay that someone is selling a brand new iPod for $150 while the local store is buying the same iPods for $170. In theory, you can buy all the iPods available on eBay and sell them all to the local store, pocketing $20 per music player. Taking advantage of this price inequality is the essence of true arbitrage.