The concept of using a babysitting service stems from a necessity intertwined with multiple facets of human life: the necessity of time, the necessity of child care, and the necessity of the trust required to amalgamate the two. More specifically, the need for professional babysitting services arises from a complex intertwining of socio-economic, demographic, and psychological elements. Furthermore, these services adhere to a particular mode of operation, backed by legal, ethical, and business principles, which aids in streamlining the process and ensuring child safety and welfare top priorities.

Professional babysitting services, at their core, offer a structured, reliable method of child care for working parents or guardians. They are operated by skilled individuals who are often trained and/or experienced in child care, child psychology, and first aid, lending credibility and an in-depth understanding of children's needs. They also provide more than just supervision; they engage children in a variety of activities, assist with their homework, prepare meals, and even perform minor household chores.

These services typically operate through a liaison system where the service provider acts as a mediator between the parents and babysitters. The process starts with a detailed understanding of the parent’s requirements, which might range from the child's age, specific needs, preferred skills in a babysitter, to the timings and duration of service. The service provider then matches these requirements with the profiles of available babysitters. The matching process often employs algorithms akin to those used in machine learning, taking into account various attributes and preferences to find the best fit.

In terms of trade-offs, professional babysitting services often come at a higher cost compared to casual babysitters. This is primarily due to the level of expertise that professional babysitters bring along with the credibility of the service. The parents are also paying for the assurance of their child's safety and personal development.

Growth in professional babysitting services can be attributed to shifts in socio-economic patterns. The rise in dual-income households, coupled with increased urbanization and the resultant time poverty, have contributed to the growth of this industry. Moreover, the advent of technology has facilitated this growth, allowing ease of access, verification, and monitoring, propelling the industry into a trajectory of unprecedented growth.

However, one must also be aware of the potential risks associated with these services. Primarily, there lies a risk of breach of trust or misconduct. To mitigate these risks, service providers often have rigorous screening processes for babysitters involving background checks, personal interviews, and reference checks. Furthermore, some services also provide continuous monitoring via technology, ensuring real-time tracking and peace of mind for parents.

Lastly, from an economic standpoint, professional babysitting services are more than just a utility for busy parents; they are, indeed, a significant contributor to the economy. They generate employment, contribute to the GDP, and, by extension, propel economic growth.

In conclusion, professional babysitting services have evolved into a sophisticated industry, marked by rigorous processes, high standards of service, and technological integration. While there are costs and risks involved, the benefits often outweigh them, making these services an invaluable asset for modern society.