Shoppers say they're seeing more requests to add gratuity at more places — even on some online orders. During the holiday season, how do you tell when to add a tip and when to skip it? Dipayan Biswas, a marketing and business professor at the University of South Florida, told CNN that "it's a relatively new phenomenon" that he sees becoming more widespread. Biswas, who's studied tipping for a decade, said the new trend started with the boom of digital kiosks. Then, the COVID-19 pandemic happened, along with inflation, which enticed businesses to allow tips to make jobs more lucrative....