I recommend EXpansys HK because they have regional offices in the UK, France, the USA and Hong Kong. Plus they will mark under declared value as SGD 300 to avoid GST. No need to re-flash rom as it's already came with oxygen os. Since it from HK, the phone should be HK set.

which should be same model as Singapore. If buy from them, remember to put remark to offset GST....
Taobao sell around $532. If add in GST will be around $569 and including Ezbuy forwarder Sensitive Air shipment wil cost around $$579.
Taobao > china warehouse > SG warehouse > you
EXpansys HK > your home.