Choosing a web specialist
Not many web designers actually do much development. You may find designers that can create awesome visual designs, but cannot set up a system with a database-driven back-end and provide the special functionality you may need.
Many developers (a.k.a. programmers) do not have design skills. They tend to create web sites that are difficult to navigate and have little visual appeal.
When looking for a web professional, you should find someone that is skilled and experienced with both. Someone that can take your site from design concept to execution and ongoing maintenance.