Each and everyone of us has a different perception and a different answer.
However, the most advisable thing would be to keep a few thousands as spare when you buy a used car. In order to cater for any expenses related to that car.
As far as your initial question is concerned, well 99% of used cars have worn out suspension bushes (unless the owner has already changed them prior to selling).
The Bushes & Steering Rack can be checked in bumpy roads at speed of around 10-20km/h . You will be able to hear and feel distinct sounds and thuds from the underbody. If you feel the thuds in your steering, most probabbly the steering rack bush has been worn out too (prefer replacing with a teflon material bush).
As for the ball-joints, arms, etc, prefer having them checked anyhow by your mechanic, since these things do tend to get worn out and might need pressing/repair or replacement as per their condition.
The "Park and press the car up and down" method works fine for shock absorbers, but for the rest, driving the car and checking its drive is the only way.
