Even if Mommy and Daddy wouldn't pay your bills in college, they would probably take over the payments afterwards until you get a job. Default on a loan would be a stain on the student's fancy new resume. Most students will do anything to preserve their credibility in the job market, and will do anything to keep making those payments. Banks count on this. They know that students get into lots of pinches and encounter lots of temptations that make irresponsible credit card use very attractive to them.
Students are likely to run up their cards.
I've seen people chained to heavy workloads because of credit debt, with work schedules that interfered with their studies until their GPAs dropped. Students have had credit problems wreck their entire academic career. Don't let them do this to you. Refuse to accept it. Talk to the manager, and tell him what you think of the bookstore's abetting of this heinous practice.