How do you vet web developers?

I'm getting ready to build a web app and I need to hire a couple of developers. I know a little about product development and this isn't my first startup (exited my last one for $40MM+). With that said, the project I'm taking on is technical and I want to make sure I hire people who will build a quality product.

When hiring I usually look at past projects and then hire devs for a small paid trial. If all looks good I continue from there, but I admit my process is a bit of a crapshoot. Curious to hear what others do to vet devs. How do you make sure you're hiring the right people for your project?

Thanks in advance. Your tips are greatly appreciated.