As a client, you decide the hourly rate for each gig. Through the app, workers can make a counter-offer if they feel a different rate is more appropriate.
In your overview of applicants, you can clearly see if a worker has requested a different rate.
Do you see a great match, but is the rate too high? Get in touch and negotiate. The worker can then adjust their offer. Once you both agree on the new rate, you can accept the worker.