It may sound suspicious, but it's totally legal.
"Retail arbitrage" happens when someone purchases an item from one merchant, then turns around and sells it somewhere else for a profit. And thanks to the popularity of online marketplaces, it's become a somewhat common occurrence.
In a small-scale test last month, CNBC ordered eight identical (or nearly identical) items from Amazon, Target and Wal-Mart. Each item was ordered four times, and sent to four cities across the continental U.S. The orders were placed with standard shipping, and without the use of membership program.
Of the 32 items ordered from Amazon, the majority of which were fulfilled by third-party vendors, six came with Wal-Mart or Target labeling or packaging.
The four bookshelves ordered from Amazon were fulfilled by three different third-party sellers. Yet each one arrived to their respective cities in packaging with Wal-Mart's labeling. The average of the four Amazon sellers' bookshelf prices was $15.22 more than Wal-Mart's price, which held steady at $68.