Most don’t like the addition of “service charges,” the amounts that many restaurants and other businesses have tacked on to customers’ tabs under various names, often to cover the higher costs of things like food and labor — without having to raise their prices.

And they are also more likely to oppose a suggested tip amount than favor it, something businesses have recently taken to putting on touch-screens at takeout spots or on printed bills — ostensibly to make calculating them easier, but often used as a prod to get customers to shell out.

But with more opportunities to tip, and with some restaurants and other businesses offering prompts, there’s still plenty of confusion about whether customers should leave a gratuity — and if so, how much.

Advances in technology — like delivery apps and tablets at counters where you can tap to leave a gratuity — might be convenient, but they are contributing to the uncertainty.

When DeSilver went looking to see what kind of guidance people were being offered, whether in etiquette guides or in popular media, the results were all over the place, he said.

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