Just emailed a place and they said its their policy that if someone has an accident they not tell them straight away and return the car seat to them , they then cut off the seat belts and replace them with new ones..
That wouldn't make me feel better about using it either The harnesses may have stretched during the accident so the new harness would be fine, but, the plastic shell may have been weakened too and not hold up again of there were another accident. I'd like to know if that practise is manufacturer approved too, I've never heard a manufacturer suggest that. SnS have a replacement scheme where if your insurance won't replace the seat after an accident they will with a brand new complete seat, no replacing the harness. I really wouldn't be confident with that at all.