This is what I do for a living and I interview writers somewhat often.

You need to find someone who sees the difference between writing as an art and as a profession. Look for someone who can research and write fast. They're not going to know what they're doing and since you're not going to get high-quality work you need to get a lot of decent work out of them.

As part of the interview process, ask them to pitch you a blog topic. Then dig deeper and find out how this post is going to benefit your business, etc. Finally, ask how long it would take them to write this blog post of say, 1000 words. The red flags are anyone who says this would take them more than 6 or so hours and anyone who can't explain the business value of their work.