It is too bad that you had such a terrible experience. Unfortunately many companies, even large ones, take advantage of their "interns" and don't give them the experience they need or deserve.

I have worked with many interns (not in sales or marketing). I always treated them as professionals and adults. i expected them to act as such. They got hands on, real experience that helped them when going for full time employment.

I only wish others treated their young people as well.