An interesting flaw (or feature?) in Amazon's marketplace

Posted by Tom Moertel Thu, 24 Jun 2010 19:59:00 GMT

Recently, I discovered an interesting flaw – or is it a feature? – in Amazon.com’s marketplace.

It all started when I bought economist Albert O. Hirschman’s Exit, Voice, and Loyalty. I had been reading an old printing from the library, but it was riddled with highlighting; now I wanted a clean copy to read without distractions.

On Amazon.com, I found exactly what I wanted. A third-party seller had listed a new copy for just $6.50. I bought it.

Shortly after the order, Amazon sent me an email confirming that my book had been shipped. In the email, the book was described as follows:

Exit, Voice, and Loyalty: Responses to Decline in Firms, Organizations, and States
Sold by: XXXXXXX
Condition: new
Quantity: 1
$6.50 each

Here’s where things get interesting. Around the time I received the shipment notice, I also received a cryptic communication from the seller:

I wish I had a pristine copy to send you but, while this book has wear at its front, I am confident it will serve you well, as it served me.

I didn’t think much of it until I received the book a week later. The book was, of course, riddled with highlighting.

Confused, I went back to Amazon.com to figure out what went wrong. I logged in, clicked on the order listing, and was shown the following summary of my order:

1 of: Exit, Voice, and Loyalty: Responses to Decline in Firms, Organizations, and States [Paperback]
By: Albert O. Hirschman
Condition: Used – Good
Sold by: XXXXXXX (seller profile)

Note that the condition is now listed as “Used – Good”, not new as it had been when I placed the order. Amazon allowed the item I had ordered to be changed after I had ordered it! What’s worse, Amazon now lists the changed item on the final invoice for the purchase.

In effect, Amazon has rewritten the history of my order. It’s as if I had ordered a used copy of the book in the first place. I’m lucky I kept that original email! Without it, how could I document what I had actually ordered?

Like most people, when I order something online, I expect that clicking the order button forms an implicit agreement between buyer and seller: in exchange for my money, the seller will deliver the product that I ordered, as it was represented to me when I placed the order.

That Amazon allows this agreement to be rewritten – behind the buyer’s back – seems like a huge flaw in its marketplace. It’s such an obvious flaw that I have a hard time believing it exists. Amazon is very good at the buyer-experience game; if it allows this “flaw” to exist, my hunch is that there must be a good reason for it. The trouble is, I can’t think of what that reason might be.

But my hunch is made more plausible by Amazon’s A-to-z Guarantee. Knowing that the guarantee will protect customers affected by the flaw gives Amazon the option of not fixing it. My guess, then, is that Amazon’s engineers thought about fixing the “flaw,” discovered a good reason not to, and decided to leave it alone.

Which raises the question, what is a compelling reason to allow a buyer-seller agreement to be changed after the fact and behind the buyer’s back?

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Baker's percentages and how not to explain them

Posted by Tom Moertel Sat, 16 Sep 2006 06:11:00 GMT

I like to bake, and I work in a professional kitchen from time to time, so I picked up The Baker’s Manual, 5th ed., hoping to carry it in my kitchen bag as a quick reference for large-scale recipes.

Before going further, you need to know two things about professional bakers. First, they measure dry ingredients not by volume, the way home bakers do, but by weight, which is both faster and more precise for the large quantities frequently used in professional kitchens. Second, when the pros write bread recipes, they express quantities in relative terms called “baker’s percentages.” Each ingredient’s quantity is given as a percentage of the recipe’s total flour weight. For example, the book provides the following recipe, referred to as a “formula,” in the section on baker’s percentages:

80.0%bread flour
20.0%whole wheat flour
66.0%water
2.0%salt
1.2%yeast

As you would expect, the percentages for bread flour and whole wheat flour add to 100 percent.

Now, here’s where the book goes down in flames. It attempts to explain how baker’s percentages let you easily scale recipes to any desired batch size, but it fails. Utterly. Here’s the book’s explanation for how to scale the above recipe to 300 pounds:

[T]o calculate the weight of each ingredient in the [300-pound] recipe, you add up all of the percentages in the above formula. This total percentage value is 169.2. Divide this number by the desired dough weight, 300 pounds, to get .564. Round this number up to get .6. Then multiply the percentage amount for each ingredient in the above recipe by .6 to obtain the larger weight required by the larger recipe. (Emphasis mine.)

When I read that explanation, I thought, Multiply? That’s the exact opposite of what you ought to do. And, sure enough, the book went on to prove its own explanation completely wrong:

80% bread flour * .6= 48 pounds
20% whole wheat flour * .6= 12 pounds
66% water * .6= 39.6 pounds
2% salt * .6= 1.2 pounds
1.2% yeast * .6= .7 pound

Note: the above is quoted verbatim from the book.

Does the “scaled-up” recipe yield 300 pounds? Nope. Add up the resulting weights and you get 101.5 pounds. Oops.

Is it really that hard to see that the correct method is simply to multiply each percentage by desired batch size and then divide by the sum of percentages? In the case of the book’s 300-pound example, we would multiply each percentage in the recipe by the following factor:

300 pounds / 169 percent = 177.5 pounds

Let’s try it out:

80% bread flour * 177.5 pounds= 142 pounds
20% whole wheat flour * 177.5 pounds= 35.5 pounds
66% water * 177.5 pounds= 117.2 pounds
2% salt * 177.5 pounds= 3.55 pounds
1.2% yeast * 177.5 pounds= 2.13 pounds

Now if you add up the resulting weights, you get the desired total of 300 pounds.

That the book not only gets the scaling method completely backward but then goes on to prove itself wrong is amazing. Didn’t anybody at John Wiley & Sons proofread the math?

Not exactly a confidence-builder for the rest of the book.

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