What should I look for in a used Proton Satria hatchback?
One thing in the Satria's favour is that it's quite reliable, despite its shoddy build quality and cheap materials.
The most likely source of an expensive repair is a head gasket failure, although cases of this are few and far between. However, it has been known to affect even the newest examples, so check the underside of the engine filler cap for water or white residue, and for oil in the coolant. Any sign of these is a warning that head gasket trouble is coming.
The Satria can also have problems with its electrics and air-conditioning system. Make sure that all the electrical gizmos (not that there will be that many, mind you, given the low level of equipment) work properly, and that warning lights don't come on for no reason. See that the air-con gets as cold as it should, and examine the pipework under the bonnet for signs of corrosion.