First thing to look at is its service history. Does it have one? Has it been serviced by a bmw dealer or specialist? Is the engine quiet? Does it drive OK? No clunks, etc. sloppy shift can usually be easily rectified. Check the rubber flexible disc - the guibo - between the gearbox and tailshaft, What's the interior like? They do not cope well with the sun in Oz. It is impossible to match the cloth and hard to get in good nick second hand. Then suspension, bushes, ball joints, etc These can be expensive. Finally look at the cooling system. The plastic/aluminium radiators can fail if it is old. Has the radiator, water pump and hoses been replaced.
BTW that first one with the non-colour coded bumper, has it had a crash at the front?
Best of luck with the search.