Buying a used car is generally a good financial choice. Buying a used car that holds its value is an even better choice. But predicting a car's value in the future can be tough: brands go out of business, technical flaws are discovered, or parts become scarce. But other cars become classics, holding — and in some cases increase — their values.

In October, the biggest aftermarket gainer was now-defunct Hummer, which increased its value at CarMax ($NYSE:KMX) by $5,652.58 on average. The company went out of business in 2010 when the market turned its back on heavy, expensive SUVs. But since then, a good Hummer has been hard to come by, and collectors are pushing its value.

Hummer far outpaced Audi, which gained an average of $617.77 in October, followed closely by Jaguar which gained $606.41.

Make

September

October

Change

Hummer

$26345.42

$31998.00

$5652.58

Audi

$27108.47

$27726.23

$617.77

Jaguar

$33097.78

$33704.19

$606.41

GMC

$27413.03

$27694.01

$280.98

Porsche

$44368.65

$44617.08

$248.43

Land Rover

$34178.10

$34375.45

$197.36

Cadillac

$29710.24

$29700.31

-$9.93

Genesis

$32279.92

$32175.15

-$104.77

Lexus

$28976.46

$28305.20

-$671.26

Mercedes-Benz

$29734.57

$28839.14

-$895.43

Among the top-10 makes sold at CarMax in October, Mercedes was the biggest loser, with an average price drop of $895.43. Lexus used vehicles lost $671.26 on average.

A single month of movement isn't necessarily a trend, but it does tell us what's happening in the auto resale market at the world's largest dealer. This new data comes after the most-expensive summer for used cars yet.

As always, we'll keep our eyes on the data.

About the Data: 

Thinknum tracks companies using the information they post online - jobs, social and web traffic, product sales and app ratings - and creates data sets that measure factors like hiring, revenue and foot traffic. Data sets may not be fully comprehensive (they only account for what is available on the web), but they can be used to gauge performance factors like staffing and sales. 

Further Reading: