If you're interested in reading an article on this, there's an interesting one by NY Times fashion critic Cathy Horyn, at http://www.nytimes.com/2008/05/22/fashion/22factory.html?_r=1&oref=slogin
The short answer is, depends on the product category. But if you mean high-end designer wear, it would be marked up at least 300%, if not more. It all makes sense when you think about what it costs to run a nice-looking place like Bergdorf's in NYC.