If the offer was made subject to finance, you can pull out, citing the low valuation as the reason.
Careful! Not necessarily. Being "subject to finance" and "subject to valuation" are
not the same thing. If you try and withdraw based on a low valuation and your finance clause, you must be careful not to say that it's due specifically to the valuation, because your contract is not subject to valuation.
You can only withdraw based on a low valuation and a "subject to finance" clause if that low valuation renders you unable to obtain finance. You need to make sure that you can back your withdrawal from the contract with rejected finance applications, in case the vendor doesn't want to accept your withdrawal and wants to take it further. If you only applied for 60%, say, and the valuation still supports you borrowing that 60% (even though that represents 80% of a low valuation, of 75% of purchase price), then you
probably couldn't get out of the contract based on your finance clause, because you can still borrow exactly what you intended. If the vendor could show that you only wanted to borrow 60%, and that was approved despite the low valuation, a court would be likely to enforce specific performance (ie that you complete the contract).
Also, depending on the wording of your subject to finance clause, regardless of the valuation and what the lenders will give you, you could even be compelled to accept vendor finance for the surplus that the bank won't lend you.
I know of somebody who wanted to borrow, say, 80% of a $500K purchase price, or $400K. Valuation came in at $400K, lender would only lend $320K. Purchaser notified intention to cancel, vendor (a developer) replied "no worries, I'll lend you the other $80K at 15%pa", and the purchaser was compelled to accept this.
This may be the case if your finance clause simply says "sufficient to complete" or something wussy like that. If it was well-written and purchaser-friendly, the finance clause would instead say something like "subject to the purchase attaining finance on terms acceptable to the purchaser at their absolute discretion".
* subject to lenders valuation being accepted by purchaser on or before date.
That, however, is an out, and a good one - nice and wide degree of latitude for you.
As others have said, I would not be interested in completing a purchase where the valuation comes in (significantly) lower than purchase price, unless, as in ianvestor's case, there are good reasons for it and the deal still makes financial sense. But generally the answer to your question is that valuations should not come in below purchase price. The vast majority of the time they come in at exactly purchase price.
If, as the agent suggests, this complex seems to always be valued under purchase price, I'd be wanting to find out why. Ring a valuer other than the panel valuer, and ask the question. They may or may not be willing to talk to you. I've found a lot of them are quite happy to "shoot the breeze".
Good luck, and hope this is all theoretical, and your valuation comes in at $550K.