How UnderSticker works
How the deal rating works
Every listing gets a rating by comparing its asking price to a data-driven fair-price range built from its true comparables. We do it in five steps:
- Estimate a fair range, not a guess. Three gradient-boosted quantile models (trained on every current listing by model, trim, age, mileage, usage and region) predict a low / typical / high fair price — so the model shows its own uncertainty instead of hiding it behind one number.
- Anchor to real peers. For models with a huge price spread (a base trim sharing a badge with a $400k halo car), we pull the estimate toward the median of the car’s own trim peers, so a base car isn’t priced like the flagship.
- Rank against comparables. We compute where each price sits among genuinely similar cars — e.g. “cheaper than 90% of comparable listings” — and how many comparables the estimate is built from, so you see the evidence, not just a colour.
- Discount for history. Cars with reported accidents, or rebuilt/salvage titles, are worth less than a clean equivalent, so we apply a condition discount — and we keep damaged cars out of the best-deals showcase entirely.
- Gate on confidence. If the band is too wide, the comparables too few, or the discount too extreme to be a clean car, we leave the listing unrated instead of guessing.
Each asking price is then placed within its fair range — which self-calibrates per car, so a volatile model needs a bigger discount to earn “Great Deal” than a stable one does:
Data & freshness
Listings are aggregated from Cars.com, CarGurus and Autotrader (with eBay Motors being added) and the same car is merged across sites by VIN. Inventory refreshes weekly, and you can request any model on demand. Prices shown are the dealers’ advertised list prices.
FAQ
Where does the data come from?
We aggregate live listings from Cars.com, CarGurus and Autotrader (with eBay Motors being added), deduplicate the same car across sites by VIN, and refresh weekly. Prices are the dealers’ advertised list prices.
What does “fair price” mean?
It’s our model’s estimate of a typical asking range for a car with the same model, trim, age, mileage, body style and region — not an appraisal or an offer. We show the whole range (not just a single number), and how each car’s price ranks against its true comparables.
Why is a listing left unrated?
When a car’s price is too far from the fair range to be a normal market swing (roughly 30%+ off), it’s almost always a branded or salvage title the history report didn’t surface — not a real bargain — so we leave it unrated rather than badge a “deal” we don’t trust.
Do you count crashed or salvage cars as deals?
No. Cars with a reported accident, or a rebuilt/salvage title, are cheap because they’re damaged — so we keep them out of the “best deals” showcase (they still appear on the model page, scored against their condition-adjusted value). We also filter out prices so far below market that they signal an undisclosed branded title.
Can I track a car that isn’t listed?
Search or pick any of our tracked models from the home page. We track a curated set of models — everyday cars and enthusiast metal alike — rather than every car ever sold, so each model has enough comparable listings for the ratings to stay accurate.
How accurate is the model?
On current inventory it lands within about 5.5% of the asking price on a typical car, and its fair range covers roughly two-thirds of real listings. It’s a guide, not gospel — always verify a specific car yourself.
Important
UnderSticker is an independent research tool and is not affiliated with Cars.com, CarGurus, Autotrader, eBay, or any manufacturer or dealer. Prices are advertised list prices, not offers, and may exclude fees. Deal ratings are model estimates and can be wrong — they are informational only and are not financial, purchase, or appraisal advice. Always confirm a vehicle’s history (e.g. via CARFAX) and condition before buying.