Before you commit to working with a graphic designer (or agency) it's important to have a way to evaluate their skills.
Here are some ideas for testing out a graphic designer to ensure the fit is right.
Gving your prospective designer or agency a small test task (aka a draft or proof) is an excellent way to evaluate them on a number of fronts.
First, you'll be able to see the quality of output they are capable of producing. Second, you'll gain some insight into how they work. For example - are they willing to ask questions to get the information they'll need to get the job done? And third - how fast are their turnaround times for graphic design jobs?
Keep in mind that some designers and agencies may not be willing to do a test task for free, so be sure to ask if they will do this for you. Don't be surprised if the designer adds a watermark (a greyed out logo) to the draft/proof so that it cannot be used for free.
A test task can be an excellent way to evaluate a designer's ability to think on their feet and solve problems. However, their past work is also an indication of the level of work they are capable of producing, so make sure to have a look at their portfolio as well.
Similar to the concept of a probationary period in a job you can have an audition period for a designer.
For example, you could agree to work with them for a period of 2 weeks, and after that time period is up you have a performance review with the designer or agency and decide whether or not to continue working together.
Working with a graphic design freelancer, team or agency is similar to any other relationship - you don't just jump in to marriage right away. It takes time to build trust, and one of the best ways to do that is with small tasks over time. After all - there's no better to evaluate a graphic design team than to actually work with them.