I play tetris too (hkgwife)

Although the law of one price holds for goods that are nearly uniform in characteristics and quality and easily traded in nearly perfectly competitive markets, many - if not most - goods are not like that. Goods of the same general type may be differentiated in important ways: a Lexus LS and a Ford Focus are both cars, yet they are very different cars, and there is no reason that their prices should be identical.