Most people already know all the benefits that hiring a virtual assistant can bring. A great assistant can free up your time, allow you to focus on money-making activities instead of day-to-day minutia, and add an organizational expertise that most entrepreneurs lack. Of course, that's assuming you find the right assistant. Hiring the wrong one can cause you grief, frustration and the desire to bang your head against a wall.

One way around this is to hire a company that prescreens applicants.

But if you prefer to do it yourself, here are five battle-tested tactics to ensure that you find the best possible virtual assistant before you make any commitments.

1. Test prospects before you even talk to them. A great way to eliminate 70 percent of potential candidates before you even begin the interview process is to give them a hidden test. Whether you post a job description online, put an ad on a freelance site or post a help-wanted ad in your local newspaper, this works very well.
   
   Write out all the instructions you have for prospective employees: to submit a resume, write about their skills, etc. Before the end of your ad, give them random directions. I like to write, "Make sure to respond to this ad with the words 'purple cow.' "
   
   This is an excellent way to find out how detail-oriented someone is from the get-go, as well as figure out how well she pays attention to instructions.
   
   You'll be stunned by how many people this weeds out from the very beginning.
    
2. Make sure to get (relevant) samples. As you know, some people like to overpromise even though they might not have the skills to back it up. Other people are eager to provide samples that often turn out to be "one-hit-wonders," such as a great article they wrote way back when.
   
   Before you hire someone, make sure you ask for something relevant to you. If you're going to have them write blog entries when you hire them full time, ask for a sample entry. If you're going to have them respond to e-mails, give them a few commonly asked questions to see how they would reply.
    
3. Find out what hours they're available. Many people think that just because an assistant is virtual, it doesn't matter what hours he works.
   
   At the same time, there's a growing trend to hire assistants from overseas--in different time zones--to save costs.
   
   If you need someone to work during your business hours, make sure he's going to be flexible enough to do so.
   
   If you want someone to make phone calls for you, host live chats on your website, take notes during training calls, communicate in real time with you, or do anything that requires an online presence during specific hours, make sure that's obvious from the start.
    
4. Don't over-commit yet. The problem with going right in and hiring someone full time is that an emotional bond is created. The person you hire may not end up filling your requirements, but you feel bad letting her go because you now like that individual as a person.
   
   Given today's economy, this is especially magnified because you feel as if you're responsible for someone's livelihood.
   
   Instead of hiring someone full time from the start, give her several small, one-time tasks to make sure she does a good job, or hire her on a probationary basis.
   
   If you choose to give one-off tasks, you can have her answer e-mails, write a blog entry or make some phone calls for you. Carefully take note of her attention to detail, how many questions she asks and how many decisions she makes on her own.
   
   If you would rather hire on a probationary basis, be clear upfront. Let your assistant know you're hiring her only for a month (or however long you choose). Make sure she knows that at the end of the time you designate, both of you will have the opportunity to evaluate each other and see how you feel about the relationship.
   
   Wording it that way eases a lot of nervousness on the virtual assistant's part and frees you from cementing yourself into anything.
    
5. Run a Google search. It's amazing how much frustration can be avoided by doing a simple Google search on a prospective assistant.
   
   Oftentimes, personal blogs, Twitter accounts or forum posts come up. Read what you find carefully. How does the person communicate? What does her grammar look like? Is she overly negative? How does she relate to people?

The right responses to all of those make a huge difference to your business --and to your stress levels.

Rachel Rofe is all too aware of the potential stress in hiring a virtual assistant. Co-owner of outsourcing company Burn Your To Do List, she has carefully prescreened hundreds of candidates in order to find the cream of the crop.