The strategy of convincing a customer to buy a higher-priced item than he or she had originally intended is called

It's called an upselling

It's a common technique that a salesman / marketing team use to increase profit with promise that the customer will get a better product or service

The example of an upselling is when you want to buy a cheap house, but the salesman manage to convinced you that buying another expensive house is good for your investment, and you buy the expensive one instead.