This is a really greyish area to be honest... re: Qld Ambulance. You can't actually book for a fitting of your own seat/capsule. They only take bookings for installation of capsules you are hiring through them. I actually asked the guy when I was returning the capsule for Elijah if he could check my seat fitting as it didn't seem right to me (and it wasn't - DH hadn't done it correctly)... now he did do it, but not overly happy as they are back to back bookings for capsule installations as it is, however he wasn't going to let me leave with it not installed correctly either. He said they aren't allowed to charge to install or check owner provided seats/capsules because they aren't allowed to make a profit.... STUPID GOVT.. could use money from charging people to fix the roads or something... anyway, they are already flat out without the extra traffic it would create if they did do this.
There are places which do installations and yes a lot of them I believe are tyre install places. Hope this helps in some way. Oh and no you don't have to use a capsule either, rear facing Aust approved seat is fine.