Most of the F430's body is made from aluminium, so rust is not an issue. However, corrosion can still occur. Look carefully around the rear edges of the front wheel arches where stone chips have removed paint and allowed oxidation. The front of the car is also prone to damage from stones, just like most cars of this ilk.
Many owners will have had a clear film applied to protect the paintwork, but you should inspect it to see that water has not seeped underneath and caused the panels to begin bubbling. If the car has no such protective coating, it's a wise idea to have it professionally applied.
You should also look closely around the windscreen, especially where it meets the front wings for signs of bubbling or flaky paint. Other places to check are along the sills where they join the rest of the bodywork and along the line of the buttresses where it blends into the rear wings.
Quite a few minor faults can crop up with the F430's exterior, so check the door mirrors are firmly located as the screw inside the door can work loose. It's easy enough to tighten but is a small pointer to a lazy or careless previous owner. The door handles can also become loose over time and will need the release cable adjusted to sort this.
While inspecting the bodywork, make sure the rear lights are firmly in place as their securing lugs can snap. This is a known weak spot among owners, so should have been sorted.
The Spider's fabric hood should be in excellent condition, but make sure you raise and lower it several times during a test drive to make sure the frame is correctly aligned. If it's not, the hood can seize when not fully open or closed.
Having checked out the bodywork that's easy to see, you should also take a look underneath at the front. The F430 was designed with a flat underside to minimise and smoothen airflow under the car. However, the front panel is prone to damage when driving on and off driveways or ramps, so look and feel for any cracks. If you can look at the car on a ramp, it's also worth seeing if the rear section is intact as some mechanics cut holes into the panel to aid access for servicing work.
PHer's view:
"The roof mechanism of my Spider often went out of alignment, causing it to get stuck in a half open/closed position."
Dr Steve Leppard