1. "What are your rates and terms?"
You might as well get this question out of the way ASAP, for both of your sakes. You need to know how you're going to plug this professional into your budget, and the writer needs to know whether this job will be worth the bother. It's helpful if the writer offers fixed per-project rates; if not, find out how you can secure a reliable estimate based on hourly rates. You also need to know whether the entire amount if due up front, whether you need to put up a deposit, or whether you're simply billed after the fact. Don't immediately reject a writer who insists on full payment in advance, though -- you may be allowed to break a large job into multiple pre-paid batches or phases.
2. "What kind of writing do you specialize in?"
Different writers typically specialize in different things, especially in larger metropolitan areas where there are lots of writers staking out their respective slices of the market. It's not unusual for a writer to focus on one type of writing project, one narrow range of industries, or one particular form of writing. For instance, I'm a generalist in terms of industry -- I can write for pretty much anybody -- but I focus on "short-form" marketing content such as website pages, blog articles, brochure content and so on. Don't feel limited if your writer says, "I only do such-and-so type for writing." The beauty of hiring freelancers is that you can keep several of them on hand, attaching the appropriate writer to the appropriate project as needed, without any impact on your full-time payroll.
3. "How well established are you?"
This is an important question because it can help predict the experience you're going to have with your writer. While rookies can and do create brilliant work, they haven't reached the point where they can point to a performance track record. It's not a matter of having written for every big name in the business world; it's an assurance that your writer has coped with a wide range of situations, worked with a variety of clients, and has developed a certain amount of professional wisdom that could prove invaluable to you for years to come. In other words, buy writing expertise, not just writing. Don't forget to ask about professional references, associations and/or certifications that can help reinforce your writer's credibility.
4. "What are your turnaround times?"
The best freelance copywriters aren't just the most skilled writers -- they're also the most professional ones. Make sure your copywriter can guarantee a specific turnaround window for each job, and don't put up with a freelancer who is all "free" and no "lance." At the same time, however, make sure your expectations are realistic ones. The busiest writers may not be able to squeeze in that rush job; some of us don't have time to accept rush jobs at all. Understand in advance what your writer can and can't realistically do for you, and you'll know you should realistically ask of your writer. The result will be high-quality work, turned in on time, every time.
Try these four questions on for size the next time you're interviewing freelance copywriters. You'll find that most of us will be happy to answer them!