Google is in the testing phase of its same-day delivery project, a practice Amazon, Wal-Mart, eBay and the U.S. Postal Service are also working to roll out. Google is forging its service with San Francisco-area retailers rather than run its own warehouses. That could cut both ways for bricks-and-mortar stores, who could sell goods via same-day selling but lose the last remaining advantage of immediacy. Google aims to use the offering to stanch the flow of ad dollars to Amazon, which is bypassing Google paid search by becoming a search engine in and of itself.