How do I check that the person at my door is my tasker?

Ask them to show their Sarwisi code (Settings → My QR Code) and scan it with your phone camera. No app or account needed. You'll see their photo, first name and initial, whether their ID is verified, and their rating. The code changes every couple of minutes, so an old screenshot shows as expired. If you booked the task and are signed in, you can confirm their arrival from that page.