This article offers a lot of sound advice on hiring a designer. As techies, we’re often out of our depth in knowing what a good designer is — often, we hire a decorator instead (or as the article calls it, a stylist).
Style is important, but it’s not the main goal of design. Design encompasses the user’s whole experience. Design is the product.
The designer is the user’s advocate. I mean that in the full political sense: they are a public defender making the case for a client.
It’s a political hire, because the interest of many employees is not aligned with the user — more so in a larger company.
Techies, for example, often want to build what’s most technically interesting. Or, we want the design to be decided, so we can implement, which we’re good at. These aren’t bad things! But they are orthogonal to the user’s needs, or worse.
We’re unlikely to question the utility of a screen, or a button, or a set of fields. We’re unlikely to say “this whole chunk of code does a disservice to the user”. Someone needs to be focused on optimizing those things, and they need to be persuasive.
Make your design hire about not just taste (which is critical) but for their ability to articulate the user’s point of view. And put them in a position to argue.