A contract . Deal with someone who is a professional. Sign a contract. It gives both parties, you and the designer, a legal basis for doing business. Make sure you know how much you will be charged for the work.
Some designers charge by the hour, some by the job.
Many ask you to pay half or a third of the price upfront, so be prepared to do that. It's business . You are doing business with someone. Don't expect free services, such as examples of what they would do with your site before you'll agree to hire them or before you pay them any money. Imagine that you own a women's clothing store.