In a way, I advocate for the same kind of laissez-faire thinking when it comes to babies--hey, watch videos of how they load up an infant on momma's lap on a moped in Tibet--you're worried about a used carseat? And I definitely think people play heavily to the fears of parents when it comes to baby gear. That's my kid, a defenseless, innocent baby; there is kind of an impulse to wrap him in bubble wrap and do every possible thing to protect him because I've never had stronger protective feelings about a living being in my whole life. There's nothing easier to exploit for financial gain than American parent-fear.
On the other hand, I get pretty frustrated with my mom, who is always mocking our new-fangled parenting rules, like putting the baby to sleep on his back so he doesn't die of SIDS, or you know, using a car seat. "Back in our day, we just put the kid in a cradle in the back seat! And we were fine!"
Yeah, YOU were fine. That's called survivorship bias. Take a look at the statistics and you will realize that there is a very good reason for all the safety gear we're expected to buy and the baby techniques we're supposed to employ. There are grey areas--used carseats, in my opinion, are in a grey area, along with breastfeeding and gosh, a whole bunch of stuff. Which is why we're having the discussion.
Anyway, pretty much all my baby gear is used, but we did buy a very cheap Cosco car seat for $45 new at WalMart, because...yeah, if you can get a brand new one for $45, why not? Although our other car seat was a hand me down from a trusted friend.