Which of the following is a common type of theft in retail services?

Internal and external theft are indeed the most common types of theft in retail services. Internal theft refers to dishonest actions taken by employees, such as stealing merchandise or manipulating transaction records to create discounts or refunds for themselves. This can significantly impact a retail establishment's profitability, and it's a concern for managers as it often occurs without public awareness.

External theft, on the other hand, involves customers stealing from the store. This is often referred to as shoplifting. Retailers deal with this through various measures, including surveillance, security personnel, and anti-theft devices. Both internal and external theft represent significant challenges for retailers, making effective prevention strategies critical.

The other types mentioned, such as systematic and planned theft, may exist but are not as foundational to the understanding of common retail theft incidents. Digital theft, although increasing in relevance as e-commerce grows, represents a different context compared to the more traditional forms of theft found in physical retail spaces. Thus, identifying and understanding both internal and external theft provides a comprehensive view of theft issues faced by retailers today.