Used baby car seats are cheap - of course! But much more important than saving money is protecting your own child. If you buy the seat from strangers, you never know if the seat has been involved in an accident. Therefore, it is better to buy the seats from friends or relatives.
Especially if you buy a used seat, you should check the seat for damage. To do this, you should remove the seat cover and check the shell for cracks or deformations. The belt should also be free of cracks, pinch marks or fraying.