What is the difference between an interior designer and an interior decorator?

That's a great question, and the answer is simpler than you might think. Many interior designers also do decoration (wall coverings, furniture choice, color ideas, decorative items, art work etc.) but an interior designer will also be able to supervise and plan out a more large scale project, including a major renovation. These days, there are general contractors who are also interior designers and window treatment firms that consider themselves decorators.

So the answer is, be less concerned with the terminology on the business card and more attentive to the professional designation of the designer/ decorator. This designation will be determined by the level and type of education that the person has, rather than what they refer to themselves as when pitching for business.