Tipping etiquette and norms are in flux − here's how you can avoid feeling flustered or ripped off

The ever-growing list of situations in which you might be invited to tip includes buying a smoothie, paying an electrician, getting a beer from a flight attendant and making a political donation. As marketing professors who specialize in customer interactions, we're researching how digital payment technologies have changed how and when customers tip. Today's tip requests are often not connected to the salary and service norms that used to determine when and how people tip.