Are the classes progressive (first week is the basic step, second week a slightly harder step) or are they on going (instructor shows a different step each week)? If the classes are progressive then find out when the series begins again. If they are on going you would definately need to go somewhere else to get the basics. If you go back, ask other people in the class what they think of the instructor and if they are not getting the steps, why not? Ask about other instructors. Once you start taking classes you'll find that other students know of other instructors. They will tell you who they think is a good instructor.
Another place to consider for lessons is the local high school or college. I started with adult ed classes at night at our local high school. They taught the basics in 6 or 7 dances. It was a great place to get started and is usually inexpensive (I think it was $40 for 8 lessons). The only down side is you may be required to have a partner.