If you have the luxury of waiting for a more convenient or bargain-friendly time to shop for a used vehicle, it's worth waiting until the market offers an advantage to buyers.
Typically, more used cars are sold in the spring and the summer, which means sellers are more eager to make a sale during the cold weather months [source: Sharifi]. This should result in lower prices and, possibly, a bigger inventory — you will have a better selection of car types, models and prices. If you can wait until winter, you'll probably pay a bit less than you'd pay in the summer.
It's also helpful to pay attention to car-buying trends in the news. Sometimes there are a lot of great new cars on the market, paired with good financing deals, and lots of buyers jump on the bandwagon. When a lot of people are out buying new cars, that also means that they are trading in or selling their old cars — creating a used car market flooded with options.
Shoppers have an advantage when they have a lot of different vehicles to choose from. It increases their chances of finding something they like — and it also gives them some room for negotiation, knowing that there are plenty of other options and they can walk away from a deal that's going sour. And it's easier to get a good price: A private seller who just bought a new car is probably eager for the money, and a dealer will be eager to move one unit off the crowded lot to make room for another.
Keep in mind, though, that this situation works both ways. If you're planning to sell your own car or trade it in toward a purchase, you might not get as much money for it as you'd like.