What types of customers have you worked with?
My most common types of jobs are designing websites that operate on a content management system (CMS). More often than not, these are e-commerce websites designed to sell products or services online and make money.
I would say personal interest and portfolio websites are a close second for most common jobs I've been assigned.
Outside of the web world, business cards and magazine print ads are the most common.
What advice would you give a customer looking to hire a provider in your area of work?
My main bit of advice before hiring a graphic designer is to know what you want. However, its not always easy to formulate the image in your head into words; but by doing the best you can, the project will be completed with as little friction as possible.