You want to know how to win friends and influence people here? Take a page from the book of OKCupid pre-acquisition. OKTrends was amazing. That stuff is crack to your target market. Look at the data. Figure out the principles behind the stuff. Figure out the Laws of Fashion. If there aren't any, and it's completely...well...fashion-driven, then drop down to the data again, and cut your advice to, "shirt x has been selling 30% more than comparably-priced shirts, and female focus groups rated it significantly more attractive than the rest of its cohort."
Without data, you're just a fashion blogger who thinks they're among easy pickings.