You can perform usability testing. This is basically done to test, from a user's standpoint, how easy it is for a user to navigate around your website and find what they are looking for. A question on a usability test might be 'Find a black men's sport jacket'. Usability testers then determine how easy it was for users to find that jacket or if they had problems finding what they were looking for.
There is also Heuristic Design Testing or Evaluations. I guess I would probably say more like evaluations. These are experts who understand usability issues and other issues that might impact end users, but that might not come up during a usability test because users don't know everything. Examples of what might come up during this kind of test include using color schemes that might be found 'offensive' in some international communities that you are targeting. Or the use of green and reds to communicate statuses....when those color schemes don't work for people that are color blind. My advice is to bring a heuristic design person in when you have mock ups of what the site will look like. This gives you a chance to make changes prior to coding.
I'm providing a link to a complany that performs these services..
http://www.humanfactors.com/home/usabili…