On what a thing costs versus what its name reminds a search engine of
Forty-five dollars was the asking price on a vintage Droz at ShopGoodwill last September, and by the next morning my resale scraper had decided the watch was worth four thousand one hundred fifty-five dollars of profit.
The scraper’s whole idea is simple, and I still think it is sound. Take a ShopGoodwill listing, take the eBay median for the same title, subtract one from the other, and if the gap is wide enough, bid. The eBay side comes from a headless browser searching for the listing’s own title, which means the comparison set is whatever the marketplace decided to show a person who typed those words.
For this watch, the comparison set was sixty-one eBay listings. Twenty-two of them were Rolex, including a Cosmograph Daytona at forty-one thousand three hundred twenty-five dollars and four Datejusts above twenty thousand. Six were Jaquet-Droz, the Swatch Group maison, running from four thousand eight hundred eighty-two up to fifteen thousand nine hundred ninety-nine. None of the sixty-one was a Droz. The four letters that made the watch a Droz are the four letters that kept it out of its own comparison, because every expensive watch eBay could reach had a name that contained them.
The median of that set was five thousand six hundred dollars and change. My formula wanted three quarters of the median minus the bid, which came to four thousand one hundred fifty-five.
A search engine is not a sample. I had been treating the eBay results page as a market survey, which is the part I got wrong, and not as what it actually is: a relevance ranking assembled for one person, on one Tuesday, on one network connection. Nothing about the page’s contents was drawn at random. The Rolex Daytona is there because it matched the words and because it is what eBay’s own business model wants a person who typed “droz mechanical automatic silver tone men s watch” to see.
I ran the same search by hand on Tuesday evening. eBay answered with Jaquet-Droz, same as it did in September: a Grande Heure at four thousand nine hundred ninety-five, another at five thousand two hundred eighty-one.
What the watch actually is. Droz is a Swiss name out of Saint-Imier, spelled Droz & Perret on the pocket-watch side, and on eBay it mostly shows up as coin-silver pocket watches — an 1880 example sitting at four hundred fifty dollars tonight, with a bare movement at twenty-four ninety-five. Vintage Jaquet-Droz does turn up too, and not always at five figures: a rare seventeen-jewel Incabloc example was listed at a hundred ninety-one. So even within the expensive brand the spread is enormous, which is its own reminder that a name is not a price.
Whether the ShopGoodwill listing is actually a Droz & Perret wristwatch or a private-label movement in a Droz case, I cannot say from the title, and the title is all the title ever was. The title carries no serial number, and on a watch the serial is the thing that decides the answer.
What a name is worth. A watch is worth what somebody who recognizes it will pay. A Droz has no market among people who know what a Droz is, and a spectacular one among people who have never heard of it and read the word as the beginning of Jaquet-Droz. My tool took the second reading and priced the first object.
That is the whole failure, and it is a category error rather than a bug. Nothing crashed. The median was computed exactly as specified, the arithmetic was correct, and the number was a faithful summary of a page of watches. It was just a summary of the wrong watches. The watch cost forty-five dollars because that is what a thrift-store box of Swiss automatics costs, and the tool told me it was worth four thousand because it had asked a search engine about the word “Droz” and a search engine, handed a rare word, reached for the nearest expensive thing.
How far this spreads. I went looking for other cases in the same database rather than trusting the one that annoyed me. Of thirty thousand and fifteen rows carrying an eBay median, twenty-five thousand nine hundred fifty-one show a positive margin, which is eighty-six and a half percent. Eighty-six percent of a market looks like money. Twenty-one thousand three hundred seventy-seven of those rows have no sold-price cross-check at all, so the one free verification the system has never looked at them.
The same filter run backward is starker. Nineteen thousand six hundred sixty-seven of the thirty thousand four hundred ninety-four items were first seen by the scrapier after their own auction had already closed, a median of six hours after the close. Every one of the sixteen thousand one hundred sixty-nine positive-margin rows sitting on an already-closed auction has zero bids on it. A four-thousand-dollar margin on an auction that ended before the scrape found it and that nobody bid on is not a margin. It is a rounding error with a decimal point.
One more artifact while I was in there. Nineteen thousand nine hundred ninety-two of the twenty thousand and three distinct queries have a single row in common: a twenty-dollar listing titled “Shop on eBay,” which is the marketplace’s own navigation button, scraped as though it were a watch. Drop that one row and the median moves in seventy-four percent of all queries.
And the arithmetic is doubled. The database sorts on median times three quarters minus price; the command-line path uses the median minus price times eighty-five percent. On the Droz row those give four thousand one hundred fifty-five and four thousand seven hundred twenty-two, and across the corpus they disagree by more than fifty dollars on thirteen hundred and twenty-eight rows. Two formulas, one meaning, and the larger one wins whenever it matters.
The repair, when I get to it. Filter the captured listings to the ones whose titles share a rare token with the query before taking a median, drop the navigation card, and make the two formulas the same function. The filter is the part that matters; the rest is cleanup. Until then the margin column is a number about eBay’s search ranking, wearing the costume of a number about a watch.
It’s October 27th, 2026, a Tuesday. The watch is still forty-five dollars. The margin in my database is still four thousand one hundred fifty-five, which is a fact about the word Droz and not about the watch.