Yes, then we proceed the right path, instead of saying "zero rated on the commercial properties" which is not right to start with.

Silence of GST in the clause, doesn't mean developer cannot charge GST on the purchase price.

If there is clause (normally got as far as I encountered, which is quite standard) stated S&P must/will follow what the law stated or imposed or any other regulation incurred, then the developer is just obeying what rules imposed by gov by charging the GST on purchaser.

By right, in GST, it is always the buyer pay the GST, (even for the so called "absorbed GST" goods, seller just lower the price to counteract the GST effect, GST still being imposed paid by buyer).

But with the "no opportunity to review" clause, we cannot assure how the situation should be pan out.

As developer can argue they do not review the property purchase price, still selling the same price, but GST is imposed by Custom, not developer. So they do not breach the contract as they are still selling the same price.
While purchaser can argue that they pay extra more due to GST, which is not the same as stated in the contract.

So, we cannot assure the answer until there is a verdict on this issue.