There's no one answer to this question since there are many factors to consider when hiring a UX/UI designer. However, some tips on finding a good UI/UX designer include:
Asking for recommendations from people you trust who have had a positive experience working with a UI/UX designer in the past.
Checking out online portfolios and getting a sense of each designer's style and approach.
Requesting proposals from a few designers that you're interested in working with, so that you can compare their services and prices.
interviewing each designer to get a better sense of their personality and whether you think they'd be a good fit for your project.