Do you have a rough idea of what work is needed to pass a roadworthy? Also, is that series two, as in, thermostat at the front of the block? $500 is a bloody bargain of a price. Considering strongly as a daily runaround.
Rust and straightness? has the car been involved in a crash?
all the easy bits to point out if they need it.. eg tyres, chips in windscreen, etc
Interior condition?