Would you use a used car seat?

I have, out in my shed, an infant car seat as well as a car seat that goes from infant I think up through toddler. The infant I got from my mom, in no accidents there, but I also believe she may have gotten it secondhand. The other I got from a lady who said she bought it but it had not been in any accidents. Would you trust that these had never been in accidents? Or would you toss them and just put a nee one on the registry? I still need to check the dates on them but thought I would see what you guys would do before bothering. I’m just not sure... I don’t want to waste someone money on a new one of the ones I have may be safe... but I also know I can’t be 100% sure. What would you do?