Explain your project. Discuss your budget. Ask how they anticipate meeting your objectives. Ask if they foresee being able to stay within your budget. Consider their communication styles, and yours.
Some people prefer to work with people whose communication style is much like their own.
Others prefer a style that is different than, but complementary to, theirs. Ask to see portfolios, or samples of work. If possible, look at projects similar to your own. If not, perhaps you need to look further. If you find that professional design services are outside the scope of your present budget, you may want to consider these alternatives.