- Machine Shop & Tool Repair Service, Castroville
- Machinery, Supplies & Equipment - Business Supplies Related, Castroville
- Machinery, Supplies & Equipment - Construction & Contractor Related, Castroville
- Management Consultants & Services, Castroville
- Manicurists & Pedicurists, Castroville
- Manufacturing, Castroville
- Manufacturing Products, Castroville
- Marriage & Family Counselors, Castroville
- Meat Market, Wholesale & Products, Castroville
- Medical Supplies & Equipment, Castroville
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- Merle Norman Cosmetics, Castroville
- Methodist Church, Castroville
- Mexican Restaurants, Castroville
- Mini & Self Storage, Castroville
- Miscellaneous Agriculture, Castroville
- Miscellaneous Government, Castroville
- Motor Vehicle, Castroville
- Motor Vehicle Rental & Leasing, Castroville
- Moving Supplies & Equipment Rental, Castroville
- Moving Truck Rental , Castroville
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