https://www.wsj.com/articles/you-wa...-awkward-etiquette-of-ipad-tipping-1539790018
Consumers face that disconcerting ritual at bakeries, coffee shops, food trucks and other businesses that use tablet credit-card readers such as Square. The devices often ask customers to make tipping decisions on the fly—with the person who just served them looking on, along with everyone else waiting in line.
There is no obligation to tip counter help, according to the Emily Post Institute, unlike sit-down service by a waiter, where 15% or 20% of the pretax bill is expected. The institute, a Vermont-based authority on manners, recommends occasional counter tipping if, for instance, a customer is a regular or receives notably good service.
Tip jars have long sat on counters, but consumers have all sorts of viable excuses for avoiding them or tossing in just a few coins, such as not having the right change, according to Michael Lynn, a professor and tipping expert at Cornell University's School of Hotel Administration. Not so, he says, with the electronic tip prompts that explicitly require consumers to opt out of gratuities. "You can't even pretend like you forgot," he says. "It clearly ups the social pressure to tip."