Tradespeople can hire too. Every tradesperson account includes the client role automatically, so you can switch which one you're using at any time from the account menu (your avatar). (Signed up as a client and want to offer services? Apply to become a verified tradesperson from your account.)
Switching changes what you see. The client view shows hiring tools (search, post a job, your requests), and the tradesperson view shows work tools (browse jobs, your applications, payouts). Notifications and jobs stay tied to the right role.
If you open a link that belongs to the other role, Blue Seal switches you to it automatically so the page makes sense.