Advantages of working with Diamonds GMAC Real Estate Here are the top 8 reasons why you should work with Diamonds GMAC Real Estate 1. Our commitment to Premier Service. 2. Diamonds GMAC Real Estate - Highly Respected in R. E. Community. 3. In business since 1978. 4. Continuing In-House Training. 5. High Caliber & Camaraderie of Personnel. 6. Convenient Office with full time staff. 7. Highly Visible Office Locations on High Traffic Streets. 8. Your Relocation Experts - city, state, national, or international.