Yes you will find that a proper valuation will be very thorough and give different results as a RPData report will give you an estimate of recent sales in the area and is very generic. Most banks who perform the valuation (depending on the panel of valuers at that particular bank) will go on the contract if it is much lower than true valuation or will do a drive by and also use RPData information, but not all. Unfortunately it is out of our hands if relying on a bank valuation for the finance, although in most cases your mortgage broker would know which valuation companies are used for which lenders product you have chosen.

In regards to the above post, most valuers will take the easy way out and choose to take the valuation on the contract price, this has happened more times then I can remember.
You could however,as you have suggested. (What if we ask the seller to get it valued independently, without informing the valuer of the contract of sale price? Would that give us any leverage?)

I would proceed as it is a bargain, you are in the position of being able to finance and I would not be worried about the valuation.
After 6 months or so, you could get an independent valuation which the investment is around $600 there abouts, as per above comment and refinance and use the already gained equity to purchase an investment property or invest in other investment products that create cash flow to pay down the mortgage.

They are just ideas.
Here is a report that I wrote on valuations, it might help you down the track
https://drive.google.com/file/d/0B6R0sWMpeDOPSDg4Sl9hYnpkYTQ/view?usp=sharing