Money Saver

My mom and I were shopping at RW&Co. She chose a brown dress perfect for a summer day or while on a road. As the sales lady, passed the bag with the new merchandise, she said: "Here u go. The bag is reusable. Bring it next time and you will get $1 off from your next purchase." My mom gave her a smirk and walk away. Then I asked her, "What's so funny?" and she replied: "I already have three other of those bags. That's $4 off right there."