Stop Craigslist from selling expired car...
Another reason not to buy/sell/give away/acquire a used carseat is because you don't know the history of a carseat - specifically if it's been in a wreck (ANY kind - large or small) that has compromised its safety (most damage you can't see). Yes, a carseat can be an expensive item to buy, but is risking the safety or life of your child more important than saving money?