There were a few incidents in Rockinham WA a few years ago where there was a couple of blokes driving around one of the main streets showing badges and pretending to be police and they were pulling people over. They eventually got caught and got into massive trouble.
Again it comes down to your own safety doesn't it? If you see someone trying to pull you over for either doing something wrong, or they believing you've done something wrong, just acknowledge that you've seen them, and pull over in a public well lit up place (if it's at night). There are heaps of servos around the place, and there is nothing stopping you from pulling into a servo where lots of peolpe are and finding out what the problem is.
I was picked up by an off duty officer a few years ago coz i was up his butt on the freeway, as he was doing 10km'h under the speed limit in the right hand lane, so he showed me his badge (broad daylight) and we pulled over ont he side of the road. Gotta say i was really mad, and i as he was getting out of his car he was having a full on go at me, so i fought back telling him either one of our speedos were out or he was an idiot for driving under the limit in the right hand lane when there was no one in the left hand lane. i told him to take down my rego and get back in contact when he was back at work and we'd sort it out then and i left him there........but i never heard from him again.
Unfortunately everything nowadays is about your own personal safety, and if you feel unsafe or a bit weary about pulling over, don't be a fool, just acknowledge you've seen them and pull over in a public place and sort it out.