I did try buying parts before from amazon and newegg sg and i still do only for certain parts that are easier to rma.
Not all are smooth sailing kind of rma. Asus, Msi & including Gigabyte needs a US address for returns. They wont be shipping it back to SG.
For cpu for both brands you can rma here but you have to wait for courier to pick up from you.
For psu, i will try to buy local. 5-15 years of warranty is hard to forgo. Not forgetting that if you buy from overseas and if you are gonna send back for rma, it will easily kill off your savings as this is one of the heaviest component to ship back. Same goes to high end gpus and you must also think that if the gpus are from the major 3 brands, you will need a US shipping address.
For ram and ssd, this is where i feel most people will end up buying. These are light items. Even to rma back, a paded envelope doesnt cost much to send back to the respective brands. Besides, there is good brands outside such as Sabrent which locally there isnt.
Casing no point, the shipping will kill you, unless they ship it free or there is a flatpacking, then yes. Or special casing that sg dont have then you may consider.