John,
I live in Sydney and have just purchased a house in Marsden. I used Karen from Property Zest. Karen has been fantastic and buys quite a few properties in the area. http://www.propertyzest.com.au/ Fee was $8800 for the full service for property under 350K. I was in the same boat as you, contemplating do I fly up and have a look myself.
In the end I think I made the right choice and I would do it again if I bought interstate. Ended up finding a place before it was advertised. 6.5% yield and slightly under valuation. Karen inspected upward of 20+ properties for me and had a great viewing system through dropbox. Get her to send you a sample.
goodluck
