As with all matters in investing, you need to be cautious when looking to take on a buyer's agent. Catalyst is 100% right, not all buyer's agents are equal. I have found a majority of businesses who call themselves buyers agents or advocates really only sell developer stock and get paid well to do so. In my opinion this is blurring the line between buyers advocate and marketing. Developer stock (even well researched developer stock) may be good for some people but I find a majority of people can do better with second hand properties, if selected properly.  

I don't know any buyer's agents in Melbourne but what you could do is ring up a couple and ask what type of property they buy for their clients. If they say new or a vast majority new, politely thank them for their time, hang up and move on to the next one.
Another option is to look at a buyer's agent with a national network. They may be able to give you a broader perspective. Ask for testimonials, proven results and what processes they have in place to ensure you receive an individualised service.