Every web client is different. Some will want control of their site and some will happily pay for changes or maintenance. Which are you?
While WordPress is pretty darn user friendly, take heed: not every web design in WordPress will leave you in total control.
Just as every client is different, there are many ways to set up a website with the WordPress platform. You can go with a basic installation on one of the many free themes that exists, or use a customized premium theme or go with a fully custom theme. All options have limitations in respect to cost, functions, usability and technical difficulty. WordPress access can also be limited by your web designer, preventing access to specific areas on the back end.
My question is Will you be happy just to have control of your ability to post new content on your blog (a given), or do you think you may want some flexibility, such as adding/removing content on your sidebar, updating your pages or maybe even swapping in a new header? Are you technically savvy enough to learn and implement doing these tasks with minimal support? Do you want to be able to pass control on to a different web designer? If you do, then make sure your project is going to permit you to learn how and do these tasks, and that your designer is willing to accommodate your requests.
During your planning process before you discuss with a web designer, make sure you know how much control you want.