Finding a good diff repair shop may be more difficult than finding someone who is honest and who really cares about doing a good job. They must also be competent.
Before having any work done, I still like to see the mechanic's work area. If the store is clean, organized, and staff are proud to show, I'm a little more comfortable. You can also visit https://www.gear-exchange.com.au/differential-repairs-sydney.html to know more about differential repairs in Sydney.
I also like to ask many questions before moving over my keys. Where do they get their parts? Do they have in stock? What kind of warranty comes with parts and labor? How long does it take to do the job? How diffs are they doing each week?
Image Source: Google
I also always insist on a precise estimate of the necessary repairs before any repair work starts. Most states have excellent laws that protect the customer by requiring all repair facilities to provide those estimates, while some states do not provide any protection for the user at all.
Finally, I recommend you to pay with a credit card. This ensures not only that you have a remedy for a problem with the shop; it also weeds stores that credit card companies will not do business with.
Another thing I want to mention is that even though I do not like to travel long distances just to get my truck worked, I found the drive to a reputable store is usually easier than the hassle of a bad repair experience.
Fortunately, there are many honest repair facilities, competent there. Be aware, they want your money as much as you do, and it never hurts to be careful and ask lots of questions.