Hire the right freelancers and you’ll be able to complete projects on deadline and under budget. Hire the wrong freelancers and you’ll end up with a disaster, one that costs you time and money.

So, how do you determine which candidates best fit your needs? You can (and should) review people’s portfolios, but if much of their work is collaborative, it may be tough to gauge their individual contributions.

Here are a few strategies for helping to choose the right freelance consultants.

• Get a referral. The best strategy for finding a qualified candidate is generally to work with someone whom trusted friends or colleagues have hired and have been happy with. Ask your network for referrals, and ask detailed questions about the work in question.

• Check references. If you can’t get a referral within your own network, look up some freelancers on your own, and ask them for reference contact details. In some cases, it’s worth digging deeper: Ben Yoskovitz, a Montreal venture capitalist, recommends directly contacting companies that a freelancer has listed on his portfolio. “You may find some surprises,” he warns. (Note, however, that if the company doesn’t recognize the freelancer’s name, that’s not necessarily a warning sign; he may have worked through an outside agency. In that case, get more details before ruling him out.)

• Come up with innovative interview questions. When talking with a potential freelancer, ask interview questions that will get him to share his perspective on how to deal with the particulars of a certain project. For instance, if you’re talking with a web developer, ask him about his content-management system of choice (WordPress, Joomla, ExpressionEngine, etc.), and talk about what steps he’d take to rebuild your company’s site on that platform. He may balk at offering you a full consultation for free, but even in a short conversation, you’ll get an idea of what his approach would be. SEOMoz offers 20 insightful questions to ask a potential web developer.
• Create a small fake project. For example, if you’re hiring a designer to create a website for your business, give her a creative brief for a fun, hypothetical project — say, ad copy for a Hovercraft. Make sure to include details about the fake company’s style guide. Because it’s not a real project, you won’t have preconceptions about how it should turn out, and it’s a good way to see how well the contractor follows direction. Although you won’t be able to use the finished work, pay the freelancer for her time: Most professionals aren’t fond of working on speculation.

• Break your project up into parts. If your project is one that can be done in several stages, come up with a plan for a freelancer to complete the first small milestone before committing to the full project. This likely won’t work for a software-development project, but if you’re hiring a writer, you can pay him for one or two blog posts before committing to a full series.