The Wall Street Journal reports…
The Journal identified several companies, including Staples, Discover Financial Services, Rosetta Stone and Home Depot that were consistently adjusting prices and displaying different product offers based on a range of characteristics that could be discovered about the user. Office Depot, for example, told the Journal that it uses “customers’ browsing history and geolocation” to vary the offers and products it displays to a visitor to its site.
It’s legal. The major factor in the price difference seems to be the distance from your zip code to a rival company’s physical store.