Scarcity can be a powerful sales motivator because no one wants to miss a good deal. It can instantly seal the deal for tire-kickers, and it can also convince people who weren’t even looking to buy now as well. But when it comes to unknown products and especially services, our first response to a big price cut, extravagant bonuses, or “limited quantity” claims is usually skepticism.

We’ve heard all about the pricing games car salesman play. We’ve heard how department stores mark-up clothing several hundred percent so they can put it on sale and still make a ton of money. And we’ve seen “limited time offers” that were still available 6 months later.

So to get the best response, your offer not only has to be great—it has to be believable. Here are three ways to do that:

1. Tell them why. We all know the saying, “If it seems too good to be true, it probably is.” So make sure you give a sensible reason for the price cut, outrageous bonuses or limited quantities.

One internet marketer’s site recently had an “I only have 197 copies made so you’d better get them fast” offer and my skepticism alarm started ringing. Why would you get 197 copies made instead of 200? That’s stupid—printing and fulfillment is always quoted in even-numbers. And why did you only have 200 made—especially since you’re always flaunting the fact that you’re a seven-figure business owner and we both know you could sell thousands of them? So I’m definitely wondering if the “limited quantity” is a lie.

2. Mean what you say. If prospects see the “introductory price” is still there six months after they first visited your site, or if they return in a month and see the same “just 5 spots left” are available–you have lost credibility with your prospect.

When I was growing up, department store holiday sales were a big deal because things weren’t discounted at other times. But when was the last time you went into a department store and nothing was on sale? They’re always having “one-day” sales (that last all weekend) and coupon specials because the only way they know how to compete is on price. But now we know if we miss one, there’ll probably be another next weekend. The motivation to “buy now” is gone.

3. Give specifics. Anytime you can support your limited-time offer with specific details, the higher your credibility will be. Having a believable number for a limited quantity offer is one example.

But to stimulate your creative juices, here’s another. A chiropractic business coach invites seven chiropractors to join him for a day to learn about his business-building system. In the letter, he explains that since he wants to keep the event small, he has only sent the package to six other chiropractors. So they need to watch the enclosed DVD (with plenty of details about what his system can do for them) and RSVP in 72 hours, or he’ll move on and contact the next seven chiropractors on his list.

But just as the gimmick alarms may be going off, he actually names the next seven local chiropractors on his list. Now they feel compelled to watch the DVD to see if it would give their competitors an edge on them, and most are persuaded to sign up for the discovery day to find out more. (And yes, when they arrive it’s just a small group of people or his credibility would be shot.)

Overall, customers can identify with the fact that you’re having a sale because it’s slow in August and they can understand if you only made 100 copies because you’re doing a trial run. So they’ll be much less likely to get hung up looking for “the catch” and much more likely to take you up on your offer.