Answer : Some do and some don't. Many interior designers do purchase furniture for their projects, but there are also a good number who work with clients to find unique and specific pieces that fit the client's needs and personality.
There are a few reasons why an interior designer might buy furniture. Sometimes they want to have more control over the look and feel of a space, or they might be on a tight timeline and need to purchase furniture quickly in order to meet a deadline. Another reason is that they might have access to better deals or discounts because of their profession.