To upsell is to get a customer who is already buying something to spend more — a bigger size, a better model, an extra service. The customer walked in wanting one thing; the seller walks them up to a costlier thing. 'Would you like to make that a large for thirty dollars more?' That is an upsell. 'Do you want the extended warranty?' Also an upsell. This is business vocabulary. You will meet it in shops, restaurants, hotels, phone companies, software companies — anywhere staff are trained and measured. Managers say 'We need to upsell more', and staff hear a target. It is a verb ('the waiter upsold us on the wine') and also a noun ('the dessert menu is a classic upsell'). Because it names a sales technique, the word carries a small coolness. Nobody says it warmly about their own experience. When a customer uses it, they usually mean they noticed the trick: 'I only wanted the basic plan, but they upsold me.' There is a slight edge of 'I was managed'. Keep it apart from 'cross-sell', its close cousin, which is selling a different thing alongside — fries with the burger, a case with the phone — rather than a costlier version of the same thing. In real speech people blur the two, so do not be surprised.

追加銷售、向上銷售（推薦更貴的規格或升級）。台灣服務業訓練裡常直接講「upsell」或「加價升級」