On Business: Light
The obvious answer to address that issue, then, is to block up the windows. Many stores I've seen plaster the windows with a variety of promotional posters and standees they get in the course of running a store. This not only blocks UV light from getting into the store, but it also serves to promote the store's contents as the posters frequently depict characters that are readily identifiable with comic books.
The downside to that approach is that, while ultraviolet light is blocked, so it visible light. You don't want customers stumbling around a store without being able to see anything, naturally, so overhead lights are added. Usually fluorescent because they tend to be more efficient for lighting stores. However, the effect isn't always the best.
(Side note: fluorescent lights do emit UV rays as well, but at significantly lower amounts than sunlight.)
Typical office-style fluorescent bulbs have a CCT (correlated color temperature) of around 4,100 K. This means that, to the eye, they have about the same color as bright moonlight. Daylight tends to start at around 5,000 and go up from there (depending on the time of day, amount of overcast, etc.). Further, without enough actual illumination, the CCT visually appears to skew downwards -- basically, that in order to make a high CCT light appear "normal" or "comfortable" there needs to be a lot of it. So a store setting which only has enough fixtures to supply supplemental light to the large picture windows at the front of the store won't appear comfortable if those windows are blocked, making the florescents the only source of light. Which means that it'll be darker than it should be in the first place, and the light that is available will appear unnaturally pale. Which means you wind up with a dark and dingy feeling store that people aren't comfortable in.
This can be addressed in different ways, and what makes the most sense would depend on the actual structure of the store itself, I think. They do make window films that block UV light, but still allow in visible light. The front windows could be covered with these relatively cheaply, but it obviously wouldn't help the lighting situation on dark or overcast days. Another option is switching to higher temperature bulbs; they do get more expensive, but I know 6,500 K bulbs are available and probably higher ones are too. A third option would be installing additional light fixtures throughout the store. This could be either more flourescents, or perhaps a series of smaller spotlights or track lighting.
The point is that, while light can be very damaging to a store's actual stock, it's still necessary in order to provide a comfortable setting for customers. This isn't something that I expect more store owners think about even after they open a store, but every aspect of a location contributes to a store's brand, and it's worth giving some consideration to both the goods that are being sold and the people buying them.