Actually you can opt for properties with Conquas status which is very strict. as the standard is strict, obviously contractor will priced it higher, which in turn will cost developer more which in turn will cost you more.

If you are smart consumer, you should ask all the questions before you committed to a property. Ask them from A to Z, furthermore, all materials are stated in S&P, if it's different from S&P, you can sued developer.

As for your example of double storey house, it is no brainer that they use sand bricks as there's no requirement for them to use clay bricks for party wall as it'll cost much more & only act as partition. BTW i don't see any problem with using of sand bricks.

Developers are about business, so it's for sure they'll maximize profit.