I believe there is a website that specializes in selling used car seats, not sure what it is though.
Its one of the things that bugs me about car seats, we used a second hand one from a freind, but obviously it was a from a trusted source. You’d think the manufactures would use some kinda of indicator to show that the car seat had undergone excessive decellaration. We use “shock watches” at work which turn red to indicate the level of G a unit has experienced, something aong those lines.
For the record, Britax Evolva. We have seat in the garage for infants upto 4 years, we never used it as it didnt secure that well. It has a system that clamps on to the seat belt which had a habit of working lose. By comparison the Evolva doesn’t budge at all.