"Many people use the terms "interior design" and "interior decorating" interchangeably, but these professions differ in critical ways.
Interior design is the art and science of understanding people's behavior to create functional spaces within a building. Decoration is the furnishing or adorning of a space with fashionable or beautiful things. In short, interior designers may decorate, but decorators do not design.
Interior designers apply creative and technical solutions within a structure that are functional, attractive and beneficial to the occupants' quality of life and culture. Designs respond to and coordinate with the building shell and acknowledge the physical location and social context of the project. Designs must adhere to code and regulatory requirements and encourage the principles of environmental sustainability.
The interior design process follows a systematic and coordinated methodology—including research, analysis and integration of knowledge into the creative process—to satisfy the needs and resources of the client.
Many U.S. states and Canadian provinces have passed laws requiring interior designers to be licensed or registered—documenting their formal education and training. By contrast, interior decorators require no formal training or licensure."
Know difference and watch out for the one who has a "knack for decorating". Odds are that's the one using its own personal taste to change your space and not the elements and principles of design and the tenants of environmental and color psychology. Be smart!