Age may or may not be a problem, but several of the people I know that have sold car seats have done so specifically because they were replacing them after they were in a vehicle collision. (Which probably also involves insurance fraud, since insurers will pay for that but require—easily faked—evidence that the seat has been rendered unsaleable, e.g., photo of it with the straps cut.)

Now, maybe they were all being excessively cautious in the replacement, but...