A colleague sent me an email today about the use of numbers. When you use a number, people are more likely to believe you. For example, if you say “a lot of people drive old cars,” that’s not as impressive as if you say “37.4% of the population drives a car that is older than 10 years.”

Of course I just made up those numbers, but if I were to say that, you’d probably believe it, because why would I use a precise number if it weren’t true? Or, put another way, using a number lends credibility to what you’re saying.

The same thing holds with sales messages. If you use a number, people are more likely to listen.

There are lots of tricks like that, and if you’re in marketing you probably know some of them.

Use a testimonial. Use a compelling photo. Use bullets and subheads in the text. On and on it goes.

If you’re trying to get one sale and be done, and you don’t care if the person actually wants or needs what you’re selling, then those tactics make sense.

But what if you want to build a brand? What if you want people to trust you? What if you want to sell a subscription, and you want the person to renew next year because they actually like the product?

In those cases, do these tactics help? If I trick someone into buying something they don’t like, I get their money today, but is it good in the long run?

I’m not only referring to sleazy sales tactics. Even if you avoid the really awful stuff, you still want to use tactics that work in your marketing copy.

How do you know if you’re fulfilling a real need with a good product, or if you’re creating a false sense of need with a marketing trick?

I’ve wondered if companies should track this sort of thing. If your business model relies on renewals or repeat sales, then tactics that get the first sale, but don’t result in long-term customers, aren’t doing you any good.

In the subscription publishing business it’s common to lose money on the first year’s sale, hoping to make it up on renewals. That assumes that the person really wants the publication and will renew. (Of course you can trick them into renewing as well, but let’s leave that aside for the moment.)

Let’s pretend that you’re in an honest business, that you believe in the value of your product and that you only want to sell to people who genuinely benefit from your magazine. You’re not trying to fool anybody, but at the same time you know that certain tactics work better. That’s not an intrinsically evil thing. If you use stupid tactics, the market isn’t going to hear your message or consider your product, which is, in fact, a good thing for them.

So where do you draw the line between “good marketing practices” and “cheap psychological tricks”? And how do you know which ones are actually helping you in the long run?

As a somewhat trite example, consider two salesmen.

The first is attractive, well-spoken and well-groomed, and closes lots of sales, but gets a lower renewal rate. People are buying because they’re taken in by his good looks.

The second is not attractive, a little sloppy and a little awkward. He doesn’t close many sales, but everybody who buys from this guy renews.

Is it worth tracking such things? How would you do it? Are you going to mark every email campaign with some sort of sliding scale of “marketing trickery”? Will you note each sales record with the attractiveness of the salesman?

It’s an interesting dilemma. The only thing I can think of is recording the response rate of the effort that brought in the sale, and then comparing that to the renewal rate.

To make this simple, assume you’re selling magazines by email. Every email effort has a response rate. You could attach the response rate of the effort to the order, then see if there is a correlation between the response rate and the renewal rate.

If you’re tricking people into buying a product they don’t want, then — all other things being equal, which they never are — higher response rate campaigns would correlate with lower renewal rates.