Answer:
The answer is: too much data
Step-by-step explanation:
If you follow Frank's recommendations, you would be examining seven factors (social media effects, personal recommendations, the book's place, the cover, customers' habits, type of cover and store's atmosphere). Some of them might even be opposing to the others, e.g. customer never read a book by that author, but likes the cover design, but only buys books with paperback covers, is in love with the store's clerk, likes romance but only reads action novels.
This is simply too much information. If you want to increase sales, it is better to focus on specific variables, or even a couple at most.