If you're shopping online, the FTC recommends you read the vendor's return policy before clicking the buy button.
Different sellers have different return policies. Some give extra time to allow returns until after the holidays. Some require returns in as little as a week. Some don't accept returns. Also, check if there are any restocking fees if you do need to make a return. Find out who covers the return shipping costs. Sometimes the merchant will do it, sometimes it's you. Find out if you can return the purchase to a physical store.