sell someone on
Convince or persuade someone of the worth or desirability of something, as in They were hoping to sell enough legislators on their bill so that it would pass easily, or Dave was really sold on that new car. [Colloquial; early 1900s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.