Baby seats have expiration dates and it’s scary how many parents fall for the emotional manipulation around that. It makes the used car seat market dead as well as hand-me-downs
Are you saying that the expiration dates are bogus? I knew that rated sports helmets and similar products had expirations, but not car seats. Maybe I'll go check the handed-down seat my son is using...
And basically all thrift stores and other used good dealers won't touch them because of the perceived liability.
I'm fine sharing our used carseat with my 6yo only child's grandparents so that they can more easily help with my nieces and nephews (2 weeks, 1yo, 3yo, 4yo, and 5yo - oof!). My wife and I know it's not been in an accident, we would not misrepresent that to the detriment of our own family.
But I would not buy one from even the most trustworthy Craigslist or Facebook Marketplace listing imaginable.
I personally would love tamper-evident components within a carseat - think "Tip and Tell" [1] but for 3-axis accelerations. Impact-sensitive product labels exist such as those at [2], but I'm not convinced that the same accelerations and crashes that would damage polystyrene impact-absorbing foam would set off a glass ampule designed to break when you drop a rental camera lens or something like that.
1: https://www.uline.com/Product/Detail/S-866/Damage-Indicators...