Items and Products

You often hear that the difference between eBay and other e-Commerce sites is that eBay sells items, other sites sell products. What does that mean?

Here’s an example. On eBay, a seller lists a specific item, for example a tackle box titled “PLANO MAGNUM HIP ROOF SIX TRAY STORAGE BOX 8616 NEW”. When someone else lists “Plano Hip Roof with 6 Trays”, is it the same product? eBay doesn’t offer much help in answering this question. On Amazon, a Plano Hip Roof has a product number B001ECQPQG assigned by Amazon (an ASIN). Everyone selling this product will be assigned that same ASIN of B001ECQPQG.

So on an abstract level, it’s easy to explain the difference between an item and a product. A product is a way of telling whether two items are the same. Suppose seller A on eBay is offering item X and seller B is offering item Y. You purchase both of them. When they arrive, you throw away the shipping containers they arrived in. If you now can’t tell which is X and which is Y, then these items are the same product.

As mentioned before, Amazon distinguishes different products by assigning each item an ASIN. They are the same product if and only if they have the same ASIN. The ASIN is somewhat like a checksum on an item: it quickly distinguishes whether two items are the same.

The ASIN system is proprietary to Amazon. What can other e-tailers like eBay do? They can employ the widely used system of ISBN for books and UPC (universal product codes) for everything else. So it seems like the product problem is really rather easy: simply use ISBN/UPC as the checksum that distinguishes products.

Well, it’s not that simple for two reasons. First, the question of when two items are the same product is slippery. For example, is the first and second printing of a technical book the same product? The second printing often has errors corrected, but still has the same ISBN. What about a product that changes its packaging? Or Coke made with high fructose corn syrup vs. sugar? So maybe ISBN and UPC don’t precisely define a product.

An even bigger problem is that even if a product has a UPC, it might not be that easy to find out what it is. Here’s an example: I recently purchased a black Kenmore dishwasher, model 1374. I couldn’t find a UPC anywhere on the dishwasher or in the documentation that came with it, so I headed to the web. A web search finds two UPCs for the 1374:

  • 13743 883049019642 (stainless steel)
  • 13742 883049006161 (white)

The extra number at the end is the color: ‘3’ for stainless steel, ‘2’ for white. As expected, the different colors have different UPCs. That’s consistent with our definition: if you received a white dishwasher in one box and a stainless steel one in another box, you could certainly tell them apart!

But I purchased a black 1374, which is 13749. I was unable to find any UPCs on bing. Google had a single hit, to a document that claimed the UPC was 13749 883049006178 (black). Should I believe a UPC that has only 1 hit in Google, especially for a product that is one of the best-selling dishwasher models? As an aside, this gives a googlewhack, which is a pair of search terms that returns a single result in Google. The googlewhack is

13749 883049006178

Another example is the cologne “L’Homme by Yves Saint Laurent Eau De Toilette Spray 2 oz”: Go to Google, click on “Shopping” and search for that title. Click on “Details” and it returns the UPC as 556779982028 and 885892085119. Which (if any) is correct? You can try a UPC validation website,

It has a hit on 885892085119 but not on 556779982028. That suggests the 885 is correct. But go to Amazon and search for “Lhomme by Yves Saint Laurent Eau De Toilette Spray 2 oz Men” (you may have to scroll down in the search results to get this: skip pass the La Nuit De L’homme items). It gives the UPC as 556779982028. Which is correct — the 885 or the 556?

These examples should convince you that although the concept of a product seems simple, it’s anything but. UPCs (and ISBN) at first appear to be an easy way to find the product for an item. But when looking more closely, we discover that we can’t reliably find the UPC, even for common products. It may not be on the product itself, nor reliably available on the web. I hope to return in a later blog posting to talk about some attacks on the problem of associating an item with a product.