A 4-day shopping tour in Delhi and a visit to the Taj Mahal in Agra sounds like a fantastic itinerary! 
 
Day 1: Arrival in Delhi**
- Arrive in Delhi and check into your hotel.
- After some rest, head to **Dilli Haat**, a famous open-air market known for handicrafts, textiles, and traditional Indian products. It's a great place to start your shopping spree and experience various Indian cultures.
- In the evening, you can explore the bustling streets of **Connaught Place** and indulge in street shopping or explore the shops in the inner circle's emporiums.
 
**Day 2: Old Delhi Exploration**
- Begin your day with a visit to **Chandni Chowk**, one of Delhi's oldest and busiest markets. It's famous for its narrow lanes, street food, and a wide range of products, including textiles, jewelry, electronics, and spices.
- Explore **Kinari Bazaar** for fabrics, ribbons, and other sewing supplies.
- Visit **Dariba Kalan**, known for its exquisite silver and gold jewelry.
- Afternoon visit to **Lajpat Nagar Market**, a famous shopping destination for traditional Indian wear and accessories.
- In the evening, you can visit **Hauz Khas Village**, known for its contemporary boutiques, art galleries, and trendy shops.
 
**Day 3: Modern Shopping**
- Start your day by exploring the upscale **Khan Market**, offering a mix of branded stores, bookshops, boutiques, and cafes.
- Head to **DLF Promenade** and **DLF Emporio** for luxury shopping and international brands.
- Visit **Select Citywalk**, a popular mall with a mix of high-end brands, Indian designer stores, and entertainment options.
- Explore the **Ambience Mall** for more shopping and dining choices.
 
**Day 4: Agra Day Trip**
- Depart early for your day trip to Agra to visit the iconic **Taj Mahal**, one of the Seven Wonders of the World.
- After visiting the Taj Mahal, explore the **Agra Fort**, a UNESCO World Heritage site that offers a glimpse into India's history.
- Optionally, you can visit local markets in Agra for souvenirs and handicrafts.
- Return to Delhi in the evening.
 
Remember that Delhi's markets and shopping areas can get quite crowded, so be prepared for that. Bargaining is common in many markets, so don't hesitate to negotiate prices. Additionally, be mindful of the current COVID-19 situation and follow any travel advisories or guidelines in place.
This itinerary provides a mix of traditional and modern shopping experiences in Delhi and a memorable visit to the Taj Mahal. Adjustments can be made based on your personal interests and preferences. Enjoy your shopping tour and your visit to these iconic Indian destinations!