Also, people in college frequently trade and buy/sell things to each other via Facebook groups and WhatsApp for a deal. I got the majority of my textbooks from other students in the college buy/sell groups. There are plenty of ways a random acquaintance could have gotten her address.
In fact, there could even be creeps lurking in those college trade/sell groups posing as a college student with something to buy from another college student.
These are just some possibilities I’m playing out in my mind.
Are you thinking that the reason that Mollie is missing is because she bought textbooks online?
Beyond university students selling books, creeps are lurking in college communities?
Are they realistic possibilities?