Re: why should I buy a 164?
Rust around the rear jacking points and trailing arm attachment points. Pretty hard to repair properly. Also rust around the leading edge of the rear wheelarches (where they are covered by the rear doors.
Depending on specification, check the heater control "stepper motors". If it has three round dials on the centre console for heater controls, you needn't worry. If it has a load of square buttons that look like they came off a space ship, it has "climate control". Make sure that you try every setting on the air distribution console (screen, face vents, footwell etc) and that the air does as it's told. Also make sure it blows hot AND cold. If it fails to do either, it's a dashboard-out job, which is not for the faint hearted!
Other than that, they're remarkably well built. Some say, the best built cars Alfa ever did!