Here is a story from my personal experience, which provides an interesting example of the “That's Not All” persuasion technique.
One day, I was doing my grocery shopping at the local Morrison's store in Leamington Spa, when suddenly an announcement caught my attention. It appeared that anyone who was willing to listen to a presentation on some fantastic new knife sold exclusively in Morrison's would get a free vegetable peeler worth £4.99 at the end. Well that was persuasive enough, who can say no to free stuff? So, off I went.
The presentation was almost a performance. The lady showed us all how this knife magically cut through a wooden chopping board, dented a piece of metal and cut effortlessly through a tomato, which she claimed would be easily squished by an ordinary knife. Needless to say, this super knife seemed rather impressive. However, the proposed price of £25 dampened mine and I'm sure a lot of other people's enthusiasm.
“But wait!” the lady said. “That's not all.”
After highlighting that the knife was sold exclusively at Morrison's (sneaky use of the “scarcity” technique I talked about in my first blog post), she claimed that if you were to buy two of these knives (God knows why one would want to, perhaps a Christmas present for that special someone?), you would get a THIRD one absolutely free (one for each member of the family?) as well as a special knife for carving meat, and a little knife, the purpose of which I don't remember.
While I'm sure the addition of a number of products to make the deal appear better value for money convinced quite a few of the customers, being a thrifty student I felt that I didn't need to spend £50 on a large set of sharp knives. The technique of “That's Not All” seems to have failed on me.
Maybe the effectiveness depends on the attractiveness of the original product. For instance, Jerry M. Burger (1986) conducted a series of seven experiments to demonstrate and explain the effectiveness of the “That's Not All Technique”, which involved selling cupcakes, something that would have definitely appealed to me. I will focus on just the first experiment here.
60 adults and teenagers who came up to one of the psychology club bake sale booths set up at three different locations on a university campus participated as subjects (20 at each booth). The aim of the experiment was to see how effective it would be to include an additional product (cookies) a few seconds after giving the price for the cupcakes.
Two experimenters sat at the bake sale table with no prices listed. The cookies were hidden from view. Subjects were given one of two responses on a random basis, when they asked about the price.
Control response: The experimenters showed the cookies straight away saying that the package of two cookies and a cupcake cost 75 cents.
That's not all response: The first experimenter would say that the cupcakes cost 75 cents, but then the second experimenter would nudge him, they would talk for a few seconds, and afterwards the first experimenter would tell the customer that actually the price included two medium sized cookies.
The results were definitely in favour of the technique, as 73% of the “That's Not All” subjects purchased the cupcake and cookies package, while only 40% of the control subjects purchased the package as illustrated on the bar graph below.
So in fact the results of the experiment suggest that a high percentage of those who watched the presentation on the magic knife in Morrison's should have bought the whole set. However, there is a distinct difference between the experiment and the event in Morrison's. This is because in the experiment, the people who walked up to the stall were definitely interested in cupcakes in the first place, whereas I am sure that some of the people who agreed to listen to the presentation had 0% interest in knives (like me) and were only there for the free vegetable peeler. Thus, despite the empirical evidence showing the effectiveness of the "That's Not All" technique, it might not have worked so well in the situation I have described.
Increasing Compliance by Improving the Deal: The That’s-Not-All Technique, Jerry M. Burger, Journal of Personality and Social Psychology, Vol. 51, No. 2, 277-283