It's electrics that are the biggest problem and parts availability. Make sure all electrical items work on any car you look at and air con, as compressors can be expensive to change.
Make sure service history is good and there's proof of cambelt and water pump changes and if an auto make sure there's proof of gearbox oil changes.
Make sure heater is working and air is consistent from all vents because of it's not it could be heater matrix which isn't a cheap job either.