I'm not sure if there's anywhere that you can take it, maybe try contacting the NRMA or RACV (or equivalent in your state)?

I sell pre-loved car seats and check the following things (after asking the previous owner if it has been in an accident of course):

* Look at the back of the car seat and check the plastic. If you see white lines/creases, this is a sign that the car seat has been under stress (accident). The plastic is designed to do this to make it obvious if the car seat has been damaged.
* Check that all the straps and harness are free from fraying.
* Check that the car seat is structurally sound (make sure parts don't appear to be loose, etc.).
* Check the year of manufacture. Car seats older than 10 years old no longer meet the Australian standards and I personally wouldn't use one. Most car seats have a sticker with the date of manufacture on it.

HTH