refactor: rewrite used car article, remove LLM confidence chat draft

hugo/eliaskohout.de/content/projects/gebrauchtwagen-datengrube.md

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+---
+title: "2 Million Used Cars and What They Tell Us"
+date: 2026-02-18
+tags: ["Scraping", "Data Engineering", "Grafana", "PostgreSQL"]
+summary: "Scraping ~2M used car listings, throwing them into a database, and seeing what shakes out."
+code: ""
+demo: ""
+---
+
+## The Question
+
+Everyone's heard the legend: a VW Passat that just keeps going at 400,000 km.
+But is it actually the only car that pulls that off? What other models quietly
+rack up absurd mileage — and what do they cost? In short: what makes a car
+*last*, and can you get one without overpaying?
+
+Time to find out with data instead of hearsay.
+
+## The Approach
+
+A major used car platform turned out to be surprisingly cooperative when it came
+to structured data. Their recommendation engine helpfully links to similar
+listings — so starting from a search, you can just keep crawling through related
+results.
+
+The haul: roughly **2 million listings** from early 2026, downloaded as JSON and
+loaded into a PostgreSQL database. Each listing carries make, model, fuel type,
+price, mileage, registration date, location, and a handful of other fields —
+enough to get interesting.
+
+---
+
+## Findings
+
+### Price vs. Mileage
+
+The obvious place to start: how does price relate to mileage?
+
+{{< grafana url="https://gr.eliaskohout.de/public-dashboards/0852019305114cd189aedb67dea27721" height="450" >}}
+
+Two clusters jump out: low-mileage/high-price (garage queens) and
+high-mileage/low-price (daily drivers priced to move). The vast majority sits in
+modest territory on both axes. The plot caps at €1M and 1M km — beyond that, the
+data is mostly typos and placeholder values.
+
+Across the cleaned dataset, averages land at roughly **€28,400** and **75,600
+km**. That gives an overall ratio of about **€375 per 1,000 km** — not a
+depreciation rate in the strict sense, but a useful back-of-the-napkin metric
+for comparing brands.
+
+### Price per Kilometer by Brand
+
+Of the **346 distinct makes**, 72 have more than 500 listings — enough for
+meaningful statistics.
+
+{{< grafana url="https://gr.eliaskohout.de/public-dashboards/1777bb018e9b47639b93ef31d97f9c89" height="450" >}}
+
+The ranking mirrors common perception — luxury brands dominate the top. But it
+has a blind spot: **age**. BYD ranks just below Ferrari and Rolls-Royce, not
+because it's a luxury vehicle, but because the average BYD listing is only **0.7
+years** old (overall average: **6.7 years**). Give these newcomers time to
+accumulate used inventory and their ratios will settle.
+
+### Depreciation
+
+{{< grafana url="https://gr.eliaskohout.de/public-dashboards/e999ce3c237b4cae95b3331331a26261" height="400" >}}
+
+Average prices over mileage for Mercedes-Benz, Toyota, Volkswagen, and Volvo all
+follow the same shape: steep early depreciation that gradually flattens out.
+Brand-level differences show in the starting points and decay rates, but the
+exponential form is universal.
+
+The first 50k km wipe out **32–39%** of value across all brands — the new-car
+premium evaporating. From 50k to 200k km, depreciation settles into a steadier
+20–30% per bracket.
+
+{{< grafana url="https://gr.eliaskohout.de/public-dashboards/a801062ca49f49d0a1ef4f97ccb550c8" height="400" >}}
+
+Grouping listings into 50k-km brackets also gives a rough "survival curve" — not
+a true survival rate (it conflates production volume, usage patterns, and actual
+longevity), but the *shape* tells a story. Volvo shows the gentlest decline: 39%
+of listings remain at 100k km, still 6.6% at 250k. Toyota drops steeply early
+but then shows a stubbornly flat tail — 51 listings at 400k, 33 at 450k. Once a
+Toyota survives the initial culling, it apparently just keeps going.
+
+{{< grafana url="https://gr.eliaskohout.de/public-dashboards/38c5b2b61b8542b4aedc91b947253991" height="400" >}}
+
+Past 250k km, the numbers get chaotic — small sample sizes let a handful of
+collector cars or overpriced outliers distort the averages. Toyota is the most
+striking case: past 250k, depreciation goes consistently *negative* — prices
+*increase* from €7,775 to €13,481 at 450k. The Land Cruiser effect: the Toyotas
+that survive to extreme mileage are the models with cult followings, commanding
+premiums *because* they've proven their durability. Past 250k, survivor bias
+takes over — the remaining cars aren't representative anymore.
+
+### The Survivors: Cars Beyond 250k km
+
+Out of the ~2 million listings, roughly **55,000** have a mileage of 250,000 km
+or more. That's about 3% of the dataset — a small slice, but more than enough to
+work with.
+
+{{< grafana url="https://gr.eliaskohout.de/public-dashboards/f9fcbcca31e64065a8e9970b88a8a999" height="400" >}}
+
+#### Who Makes It This Far?
+
+In absolute numbers, the usual suspects lead: Mercedes (8,900 listings),
+Volkswagen (8,200), BMW (6,700), Audi (5,300). Together they account for over
+half of all high-mileage entries. Renault's survivors average 362k km — the
+highest on the list — and BMW and Porsche carry remarkably high average prices
+past 250k (€24,600 and €27,300), hinting at maintained enthusiast cars rather
+than beaters.
+
+{{< grafana url="https://gr.eliaskohout.de/public-dashboards/6c4d0d116ba746f18c908ff5d4037da8" height="400" >}}
+
+But raw counts are misleading. More telling is what *share* of a brand's
+listings are high-mileage. That flips the picture: **Saab** leads at **32.6%** —
+almost one in three. No new cars since 2012 means the surviving inventory is old
+by definition, but it also speaks to owners who keep these cars running well
+past their expected shelf life. Iveco follows at 21% (commercial vehicles, no
+surprise). Then a cluster at 5–6%: **Volvo, Honda, Subaru, and Mercedes-Benz** —
+the brands enthusiasts *claim* are built to last, and the data is at least
+consistent.
+
+Notably absent: **Toyota**. Only about 2% of Toyota listings cross 250k — below
+the dataset average. That doesn't mean Toyotas die young; they may get exported
+or simply leave this platform. The data can't distinguish "the car died" from
+"the car left the market."
+
+#### Diesel vs. Petrol
+
+{{< grafana url="https://gr.eliaskohout.de/public-dashboards/b721ad75bf764693ba6243714899e0f0" height="400" >}}
+
+Diesel dominates the high-mileage segment: **6.75%** of diesel listings cross
+250k km, compared to just **1.58%** for petrol — a 4× overrepresentation. That's
+consistent with the "diesel lasts longer" narrative, though not proof: diesel
+cars also tend to be driven more (company cars, long-distance commuters).
+
+The real outlier is **CNG at 10.52%** — higher than diesel, though from a small
+sample of 5,500 listings (mostly fleet cars and taxis). Electric cars and
+hybrids are virtually absent at 0.07% and 0.16% — simply too young to have
+accumulated that kind of mileage.
+
+#### What Do They Cost?
+
+{{< grafana url="https://gr.eliaskohout.de/public-dashboards/543b7c49e5f742468f1d90b112cec799" height="400" >}}
+
+**Porsche** stands alone: a median of **€21,000** even past 250k km — these are
+maintained sports cars that appreciate regardless of mileage. **Land Rover**
+(€11,000 median) and **Iveco** (€12,000) also hold surprising value — cult
+status and commercial utility, respectively.
+
+Most brands cluster in the €3,000–€8,000 range. At the bottom: **Opel** at
+€2,650, **Peugeot** and **SEAT** at €3,000 — the genuine bargain-bin survivors.
+
+---
+
+## So What Should You Buy?
+
+Two million listings, a few dozen queries, and a lot of scatter plots later —
+what's the actual answer?
+
+It depends on what you're optimizing for.
+
+**If you want the car that refuses to die:** look at diesel Volvo, Mercedes, or
+Subaru in the 150–200k km range. These brands show up disproportionately at
+extreme mileage, and their survival curves decline more gently than most. A
+diesel Mercedes with 180k km on the clock isn't halfway through its life — it
+might be a third of the way.
+
+**If you want the best deal per remaining kilometer:** the sweet spot sits around
+100–150k km for most brands. The steepest depreciation is already behind you
+(that 32–39% first-bracket hit), but the car still has plenty of mechanical life
+left. Volkswagen and Opel are the value picks here — median prices in the low
+single-digit thousands, well-understood mechanicals, and parts that are cheap
+and everywhere.
+
+**If you want something that holds its value no matter what:** Toyota and
+Porsche. Toyota's prices actually *increase* past 250k km — the Land Cruiser
+effect — and Porsche commands a €21k median even at quarter-million mileage.
+You're not buying depreciation; you're buying into a secondary market where
+demand outstrips supply.
+
+**If you just want cheap and functional:** Opel, SEAT, or Peugeot past 200k km.
+Median prices between €2,650 and €3,000. Nobody will envy your car. Nobody will
+steal it either. And it'll probably keep running.
+
+One thing the data can't tell you: the condition of any *specific* car. Averages
+are averages. A well-maintained Fiat at 300k km will outlast a neglected BMW at
+100k every time. The numbers here describe the market, not the machine in front
+of you. For that, you still need a mechanic — preferably one who doesn't own a
+dealership.