upsell
The "art" of tacking on high-priced options to an existing sale under the guise of customer service.
Every time Bill turns on his Sprint phone, it tries to upsell him on their backup service.
upsell (verb)
An attempt to persuade a customer to purchase a more expensive item or to purchase additional items so that the total cost will be higher.
Theater staffs have developed the technique of 'upselling,' or convincing patrons to buy larger sizes of popcorn and drinks for a discount