There should be a “script” that the store has written up for you to read and go by. Ask your manager if there is one. You shouldn’t memorize it and go word for word, but make it your own words with the important points still in your speech. But don’t make it sound like a speech. Start off with the “money saved” point. “Would you like to save 15.00 off of your purchase today?” If they shoot you down right then, don’t pursue it. You will just make them angry. Also remember, people are just not interested in having more credit.