By Dean Rieck, direct mail copywriter
No matter how powerful your direct mail might be, it is still just a bunch of paper that arrives in the mailbox. Trusting a handful of paper takes a leap of faith, especially if the recipient has never done business with your company before. 
To help people make that leap, you need to do whatever you can to establish credibility and reduce the perceived risk of making a purchase. 
One of the best techniques is to include a guarantee. A guarantee can be one of your most powerful selling tools. It’s proof that you’re reputable. It helps lower perceived risk. And it almost always boosts your response. 
Here are some tips for writing a rock-solid guarantee and using it effectively in your direct mail. 
• Keep it simple. There are many ways to enhance your guarantee, but your basic guarantee copy should be clear and strong, leaving no questions unanswered. Here’s the classic guarantee: “If you are not completely satisfied for any reason, just return your widget to XYZ Company within 30 days for a full refund of your purchase price.” 
• Make it visible. Add it to your sales letter call-to-action. Highlight it as a box in your brochure. Feature it on the order form. Call attention to it with a stand-alone insert. 
• Use guarantee copy to sell. For example, you might add a line such as “Fill out the order form and mail it today. Try your gizmo for 60 days. If you’re not completely satisfied …” and so on. 
• Try unconditional guarantees. They’re stronger than conditional guarantees and easier to administer. However, if you have to use a conditional guarantee, a longer term is better — a 60-day free examination is better than 30 days, for example. Often people don’t think that a month is long enough to avoid payment if they change their mind. 
• Use strong language. “Unconditionally Guaranteed.” “No-Risk Guarantee.” “100 Percent Satisfaction Guarantee.” “No-Questions-Asked Guarantee.” As long as it’s believable, the stronger your guarantee, the better. 
• Go beyond money-back. How about “Double Your Money Back” or “115% Credit” for another purchase? Or maybe “We won’t cash your check for 30 days” or “We’ll return your own check to you” to assure that the customer will never have money at risk? 
• Match your offer. Provide a money-back guarantee for purchases, a buyback for collectibles, cancellation privileges, and a refund for subscriptions. Think of the characteristics of your offer and the perceived risk involved, then formulate your guarantee to match. 
• Add a signature. Nothing shows your commitment to a product like signing your name to the guarantee. The person of highest authority, or the person who wrote the letter, should sign it.
• Extend the guarantee period. Instead of 30 or 60 days, how about a one-year guarantee? Or a lifetime guarantee? After a while, most people forget about the guarantee or feel too guilty to return “used” items. 
• Make it look official. Certificate borders, certificate paper, watermarks, icons like eagles and flags, dollar values in the corners, and other touches can help your guarantee look official. You can even create a seal or stamp with your basic guarantee copy in it. 
• Add third-party approval. A Good Housekeeping seal of approval or an endorsement from an organization can power up your guarantee. 
• Offer a valuable bonus. For example, “If you don’t like TaxSaver Software, send it back at our expense, get a full refund, and keep the Day Planner and mouse pad as our gift to you.”
• Try extreme specificity. State your guarantee, then give a phone number to call if the customer has a complaint. You could even give the name of the person to talk to. This costs you nothing and raises the believability of your guarantee to its highest possible level.
Spend time with your guarantee. Think about it as a central element in your direct mail. How can you make it stronger? More dramatic? A benefit for customers? Your options are unlimited.
—Source: Dean Rieck has been called the best direct response strategist and copywriter in America. For more copywriting and selling ideas, sign up for Dean’s FREE direct response newsletter or visit Pro Copy Tips to get copywriting tips for smart copywriters.