Although I've observed that there are many people interested in retail establishments - evidenced by blogs like Sky City: Retail History, DeadMalls.com, Labelscar, Carolina Circle City, and Malls of America, but I generally haven't seen any concise terminology to describe the interest in retail establishments.
People that love trains are known as railfans, and people that love studying roads are roadgeeks, but I've observed no equivalent term for those that love retail establishments.
Several years ago, a friend and I actually did invent terms to be used to describe such people. In early 2013, we both came up with the term "mallgeek," and later, on December 22, 2013, I came up with the term "retailgeek." "Mallgeek" and "retailgeek" are nouns to describe people interested in such retail establishments, while "mallgeeking" and "retailgeeking" describe the interest in retail establishments in general.
"Retailgeeking" is a general, umbrella term - referring to a general interest in retail establishments. For example, one could be fascinated by Walmart, Pizza Hut, Wolf Camera, or any other retail establishment.
"Mallgeeking," on the other hand, is a subset of "retailgeeking" - used to refer to a specific interest in enclosed shopping malls.
One can be a retailgeek without being a mallgeek, or in other words, one can have a fascination with retail establishments in general without having a particular fascination with enclosed shopping malls. On the other hand, while one technically can't be a mallgeek without being a retailgeek, one can have more of a fascination with enclosed shopping malls than with other types of retail establishments. I personally tend to be more of a mallgeek, but I am also very much a retailgeek as well.