Edde: Yah, that's the part 4.. GST is imposed by the customs in SG, nothing to do with either vpost or cwg.
In general, if the purchase with a particular merchant is more than SGD400, then you incur gst. But there is a way to avoid this.
Vpost: Keep each order below SGD400 with a safe margin for FX fluctuation, usually USD230 is ok. QQ was very lucky to miss by SGD0.05!!!
For vpost, each parcel sent to your suite (in the USA) will have to be matched with a corresponding invoice you sent them. This is the trick. If you order 3 batches from vpost, send in the invoice one by one, wait for the first parcel to be matched with the first invoice and pay the shipping. When this is done, then send in the second invoice and repeat the process. This way, you won't kenna gst, but you have to pay base charge for each shipment. So got to do a calculation to see which is more worth it.
For cwg: More tricky but essentially same thing for cwg. Keep each batch below SGD400. Then send in the invoice separately. Cwg will want the user to send in the invoice before the shipment reaches them (we know this cos the merchant will always provide a tracking number). So it's more tricky to use cwg in this regard altho cwg is cheaper than vpost.