The two Bay Area companies are testing “buy” buttons, moving one step closer to generating meaningful retail sales after years of collecting information on consumer shopping habits, analysts said. If customers want to purchase the product, they click the button and enter their credit card information directly on the social networks without having to go to the retailer’s website. “This is a way to capture people when they are potentially interested in making a purchase,” said Debra Aho Williamson, a principal analyst of social media at eMarketer. The luxury brand gave customers a chance to buy the nail polish colors that the models were wearing as they walked down the runway. Other organizations including San Francisco nonprofit Glide are using the button on Twitter to sell $15 hats and raise awareness for its volunteer program. [...] Cara Bloomer, a digital copywriter at Zimmerman Advertising, is skeptical about Twitter’s button, calling it “a poor attempt at masking instant gratification with social shopping.”