Dev log

Why a coupe and a cabriolet can't be the same car

Two listings. Same year. Same engine. Same price band. Same brand. My matcher thought they were the same car. They weren't even close. Here's what I changed.

One of the things AllCars does behind the scenes is figure out when the same physical used car in Cyprus is being advertised in more than one place. Sellers do this all the time — same car, three ads, three slightly different prices. The matcher merges them so you see one car, one price history, instead of three copies cluttering up your search.

Most of the time the matcher is good at it. One day, two listings got merged that absolutely should not have been. Same brand. Same model name. Same year. Same engine size. Same approximate price. Five out of five "yes" votes. The problem? One was a coupe and the other was a convertible. Two different cars. Two different bodyshells. Same model name on the badge.

Soft signals can be talked into anything

The matcher used to weigh up "soft" facts — price, mileage, engine, year — and decide if the overall vibe matched. The way it was wired, enough soft signals could outvote anything. Including the obvious physical fact that a hardtop and a soft-top aren't the same car.

The fix was a class of hard-veto signals. Body type. Fuel. Year. Colour. If two listings disagree on any of those — and both sides are known — the merge is rejected, end of conversation. No amount of "but the price matched!" overrides physics.

What this means when you're searching

You see fewer ghost duplicates. You see fewer "wait, that's not the same car" moments. The price-history chart on a vehicle stays clean instead of flicking between two cars. And the deal score is computed on the actual car, not a Frankenstein of two.

It's the kind of fix nobody really notices when it's working — which is the point. AllCars is supposed to be the place where you stop second-guessing what you're looking at.