I agree with the posters who mentioned the renders not being on par with the best. I also agree with the poster who said the clothes weren't necessarily doing you any favors—as a whole, they're not pretty clothes. They are in most cases realistic, but I'd look at what DAZ does with Belle and their other teens, clothing-wise. Like most of the adult characters, they're wearing swimsuits or lingerie for the cover tile, but its age-appropriate, with more coverage. The additional renders show contemporary clothes. The ones you have feel dated.

The other thing you do—which is commonplace in the Renderosity store—is overload the cover tile image with ugly text. It looks like it was done in Word and doesn't look professional. Not everyone is gifted with type layout skills, but I'd find a font that has some teen spirit to it that remains easy to read. Keep the text on the cover tile minimum, and then work to declutter the inner panels. Again, look at what the top vendors are doing. 

Finally, I like the Reese Sisters more than Tina—more versatile, less like an existing product—but on one of the inner panels, you identify their ages as 23, 25 and 29, which is clearly wrong. None of them look that old and the youngest one is a tween at oldest. Since your big selling point is their age (since there are fewer teen figures), you want to make it clear you know what teens look like. Mislabelling them makes it look like you might not have used any references.