I worked in car audio for 20+ years. Nearly 2 of them in Perth, but that was a long time ago.
I recently went looking for an installer to do a few things for me here in Adelaide/ And it wasn't easy to find someone I would trust.
I started by doing a bit of a call around to thin down the list. Then went to each one left and did a bit of an interview, looked at their work ( the installers own car is a great place to start) and finally found one guy I felt would be OK. There aren't that many good audio installers around, most guys make their money doing parking sensors, dash and reversing cameras these days.
I don't know who's who in Perth these days, but Alberts never were that good, and it was very hard for anyone to compete against them ( partly because the parent company was also an importer of various brands)
I would start by looking for Focal dealers, I know the distributor and he is careful about who he lets have the product.