While one-quarter of the visits to e-commerce sites occur on mobile devices, only around 15 percent of purchases do, according to data from I.B.M. According to Google, 85 percent of online shoppers start searching on one device — most often a mobile phone — and make a purchase on another.
At eBay, one-third of the purchases involve mobile devices at some point, even if the final purchase is made on a computer. Once shoppers log in on a device, they do not need to log in again. Their information, like shipping and credit card details and saved items, syncs across all their devices. If an eBay shopper is interested in a certain handbag, and saves that search on a computer, eBay will send alerts to her cellphone when a new handbag arrives or an auction is about to end.