Buying a used car in America has come a long way since physically going from lot to lot searching for a dealership that has the right vehicle and isn't going to sneak in additional overcharges.

In the internet age, prospective buyers can search for the exact make, model, trim, color and other features of their ideal used car, which quickens the buying process with the right research.

Two of the biggest websites for this are Carmax ($KMX), the country's largest used-car retailer, and Cars.com ($CARS), the world's second largest automobile classified website. Historically, this time of year (pre-Holiday season) sees dealers list more inventory than they do, whether to clear out old models or make space for new vehicles from production facilities or auction lots, making now a timely comparison.

Carmax lists about 60,000 vehicles on its website on any given day, allowing customers to see what's in stock at their 150-plus locations.

(Note: Dates with duplicating entries removed for chart accuracy)

That, however, is peanuts compared to what Cars.com has on its website. In fact, on November 1, there were nearly 26 times more vehicles listed on Cars.com than cars on Carmax.

Of course, this data reflects the purpose for both of these websites. Cars.com, by design, is a "classified" website, similar to that section of the local paper advertising used cars. It shows car listings from all dealers, including businesses and individuals, and offers new car sales as well.

Meanwhile, Carmax is the dealer. It only lists cars from all of its retail locations (so no private sellers), and focuses mainly on used car sales (with a few exceptions.

With that in mind, the average mileage of used cars at both websites is a stark contrast. The average car on the Carmax lot has over 15,000 less miles than the average car listing on Cars.com.

Furthermore, the average price of used cars on Carmax is slightly lower than that of the average used car on Cars.com, or more specifically, a $1,000 to $2,000 difference.

Much like inventory size, differing mileage and pricing can be linked back to the business model behind each website. Because Cars.com has listings from all dealers who list on the website, rather than what's available on a Carmax lot, there are more outliers that can weigh price and mileage up. There are still plenty of vehicles that are similar to what one would see on Carmax, but there are also listings for a $300 1996 Chrysler Town & Country van that's seen better days.

That can also be seen when comparing at the most expensive vehicle makes from each service, as well as some more common brands from both websites.

Make (Carmax) Price (Average) Mileage (Average in Miles) Car Count (As of 11/3)
Tesla  $77,748.00  19,916.67  24
Porsche  $47,974.28  31,395.68  278
Land Rover  $38,069.53  35,074.66  884
Genesis  $37,078.00  20,480.00  50
Jaguar  $31,649.50  30,146.44  478
Cadillac  $28,334.53  37,956.03  1,774
Audi  $28,311.36  34,332.84  1,340
GMC  $27,490.65  44,667.99  3,030
Lexus  $26,747.08  41,450.17  4,154
Mercedes-Benz  $26,447.51  33,702.93  2,868

Make (Cars.com) Price (Average) Mileage (Average in Miles) Car Count (As of 11/3)
Bugatti  $1,472,128.57  7,288.90  20
Saleen  $429,900.00  6,764.00  2
Spyker  $302,800.00  7,125.67  12
McLaren  $276,466.15  4,779.57  742
Lamborghini  $242,203.78  9,492.13  1,100
Ferrari  $204,380.46  12,140.69  2,886
Rolls-Royce  $197,815.23  18,510.79  910
AC  $130,769.17  4,313.00  16
DeTomaso  $128,277.86  25,683.14  14
Bentley  $117,623.17  24,250.49  2,366

The conclusion? If you are shopping for a used Aston Martin or Rolls-Royce, or want to look thorugh a larger set of potential used vehicles, Cars.com is the way to go. If you want a reasonable car from one specific and reputable dealer, then Carmax is for you.

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