If someone knocks on your door claiming to be a College of Southern Idaho student or club member selling books, they are frauds.  According to CSI's Facebook page,

Incidents such as this occur quite regularly. CSI students, whether individually or as members of any of our clubs or organizations, are never sent door to door selling anything.

If you buy a book from a door-to-door salesman who claims to be from CSI, do so at your own risk.  They are not students from the College of Southern Idaho