How to tell if a used car's mileage was rolled back

Does this really happen in Portugal?

It does. carVertical analysed the vehicle history reports bought in Portugal between January 2024 and March 2026:

Source: carVertical, via Automonitor (13 May 2026). These are cars whose buyers ordered a report, not every car for sale.

Most cars haven't been tampered with. But a car hiding 99,000 km is worth far less than it looks, and may have major maintenance coming up. That's why it's worth checking.

How to check, step by step

1. Ask for the number plate and the VIN before you go to see the car.

   You need both for the next steps. A polite message is enough: "Could you send me the plate and the VIN?"

   Why it matters: the VIN is the car's 17-character chassis number. It identifies the car in any country.

2. Ask IMT for the inspection certificate.

   Request it on IMTonline, under Veículos, or at an IMT counter. It costs €30 at the counter, with 10% off online. You need the plate and a reason for the request.

   Why it matters: it's the only official record of the mileage over the years. Each periodic inspection notes the km on that day.

3. Check the km only ever go up.

   Read the inspections in date order. The mileage should never drop, and the figure in the ad should be higher than the last inspection.

4. If the car is imported, look up its history by VIN.

   Services such as carVertical or autoDNA gather records from other countries: mileage, past owners, inspections. Full reports are usually paid.

5. Ask for the service book and invoices.

   Each service and workshop invoice usually shows the km on that day. "Are there service invoices?" is a normal question; a seller who kept the car up to date usually has them to hand. If they're missing, a brand dealer can often see the services done in its network from the VIN.

6. Check the wear matches the mileage.

   A smooth or shiny steering wheel, a worn or sagging driver's seat, worn pedal rubbers, a gear knob with its texture gone. On a low-mileage car, these usually don't show yet.

7. Compare the price with similar ads.

   Same model, year and engine. A car much cheaper than the rest with lower km is a reason to ask for more evidence, not to rush.

Reading the certificate: an example

Illustrative example, not a real car.

The ad shows fewer km than the 2021 inspection. The numbers don't match. It could be a recording error or something more serious: ask for an explanation and documents before you pay anything.

What the certificate tells you, and what it doesn't

• It tells you: the km at each inspection carried out on the mainland.
• It doesn't cover: the first 4 years. Passenger cars have their first inspection within 4 years of registration, then every 2 years until they're 8, then every year.
• It doesn't cover: inspections in the Azores or Madeira. Those are requested from the regional transport offices.
• It doesn't show: what happened between two inspections. A tidy sequence helps, but it doesn't prove everything, so cross-check it with the invoices and the wear.

Common mistakes

• Trusting the odometer alone. The number on the dashboard is the part that can be changed. The evidence is in the records.
• Assuming a digital or recent car is safe. Electric and hybrid cars show up in the data above too.
• Accepting "the service book got lost" and nothing else. It may be true. Ask for the invoices instead, or confirm by VIN with a brand dealer.
• Looking only at the km. A high-mileage car with documented servicing can be a better choice than a low-mileage one with no history.

Where Compadre fits

If you're looking at an ad right now, paste the link into Compadre. It reads the ad, lists what's worth checking for that engine and mileage, and gives you the questions for the seller, including the ones about the certificate and invoices. The preview is free and you don't need an account.