Never trust a land agent Gaz. I deal with this shit everyday and somehow even got stung myself.
Always take the time to invest in having a solicitor/conveyancer and/or surveyor advise you before committing to a block. I highly advise you get your own contours and soil report prior to purchase also. The developer supplied contours we received were incredibly lenient compared to our actual contours report from the surveyor...approx 500mm diagonal fall off among other misrepresentations! Land agent also advised of M class soil, when our report came in at H1. You're looking potentially at $1,500 - $3,500 just in the altered slab design there.
On another note, let me know when you do purchase a block. I might know a quality builder that will happily provide you a quote...