I found out that 96% of child restaints in NSW are installed incorrectly. And studies have also shown that lat year 1600 children were either seriously injured or killed because they were in a car accident and there child restraint was not fitted correctly. This information came from a RTA Authorised Fitting Station and apparently you can be fined up to $250 and loose 3 points if a child restraint is not fitted correctly.
These Authorised Fitting Stations charge about $30 to install one and about $15 to check one that has already been installed (if you have done it yourself). You can even have them come to your home for about $50. Its not a lot of money for piece of mind really.
I think if you pay attention to how they do it and keep notes especially if you have to do it often you would at least get the right method from scratch and like someone said the more you do it the better you would get at it.