Why user test?

So you’re paying for a reputable web development firm and they’ve convinced you they know all about usability, so why should you pay for user testing?

Surely if the developers are the experts, you don’t need to pay for additional user testing, right?

Wrong!

Usability experts will design web pages based (hopefully) on many years of experience of what works and what doesn’t work and with any luck with some formal HCI training.

They normally get it pretty much right, but they’re still guessing or hypothesising (admittedly on years of experience) on what will work, what will be easy for users to do and what will confuse them.
The problem is, that it is still a best guess. Even with a perfect IA (information architecture or site layout) and perfect wireframes (blue prints for the functional elements of a page) and great visual designs, there’s still a heap that can go wrong.

Common problems include; key calls to action which are not obvious enough, or do not stand out enough, insufficient contrast between text and background making it hard for users to read certain page elements, distracting visual elements which detract from the main action you want people to do on the site, incorrectly perceived groupings of things that look related through proximity or colourings and of course the exact opposite, related items which user’s don’t see as being related to one another (this is particularly true with users understanding where they are within a site’s structure).
It isn’t until the site is designed, built and populated with final content that you can truly test the site and ensure that users are taking the actions you would like them to take on your site.