To determine the value of diecast cars, look up the cars in an online price guide or a price book for that type of diecast car. NASCAR diecast car price guides include DiecastRegistry.net and "Becketts Racing Collectables Diecast Price Guide," while "Tomart's Disneyana Collector's Guide to Disney/Pixar Cars" has prices of Pixar diecast cars as of 2015. Alternatively, look up completed auction results for the diecast car on eBay or other auction sites.
Factors that affect the value of a diecast car include the manufacturer, rarity and scale. The manufacturer affects the value because some manufacturers create more detailed and more expensive diecast cars than others, making their cars more valuable. Rarer diecast cars tend to be more valuable, and the primary factors that affect rarity are the amount produced of a specific diecast car and its year. When fewer cars are produced, there are fewer in circulation, which makes them more valuable. Older cars are also usually more difficult to find, adding to their value.
Diecast car scales include 1/64, 1/24 and 1/18. While 1/18 are the largest and have the most detail, people don't collect them as often due to their large size. Most collectors focus on 1/24 scale.
While price guides have the value of diecast cars, these fluctuate frequently. The actual price someone pays for the car is difficult to predict, since diecast cars are collectible items and therefore only valuable to people who collect them.