In Hollywood, the promise of social media was that it would enable celebrities to communicate directly with their fans and expand their followings. The reality of social media is that it’s become a major channel for advertisers to target consumers. And unless you’re really paying attention, you’ll be hard-pressed to know whether what you’re reading is a real opinion or a marketing message (bet on the latter). From the NYT’s Sapna Maheshwari: Paid $75,000 to Love a Brand on Instagram. But Is It an Ad?