I have another thread on here about PayPal Checkout.
On the first page, there`s some links to good research articles about how people shop online.
Although I`m not your market because I totally would never buy designer clothes for myself let alone my kid .... (I did quick lookieloo, said WHOA on the prices, and left ... so I`m one of your non-shoppers!)
I would suggest that your site be, well, more upscale for your more upscale clients? Kind of like how expensive department stores have nice couches ... you need something that says "come on in and sit a while".
You also have to consider ... do people in your market shop online, or are they more likely to just go to Macy`s? If they do shop online, how do they find you? Can you find other sites that sell very high-end clothing or luxury items online and talk to them about how they do it?
I would imagine it might be hard to sell such things on eBay as well, where people are looking for a total bargain.