Auto body repair & detailing: Rusty Bolts, mitsubishi galant, rusty bolts

Question
I am currently looking to buy a 2005 Mitsubishi Galant. I had my mechanic look at it. Everything checked out fine only thing he was worried about was under the hood some but not all the bolts were rusted. He told me to do a carfax on the vehicle to see if it had been in a flood. No flood or salvage was found on the report. What causes this and is this something I should be worried about?

Answer
IF SOME BUT NOT ARE RUSTED ARE THEY AT THE SAME /APPROXIMATE HEIGHT?
IF NOT I WOULDN'T WORRRY. CARFAX HAS NOT REPORTED ANYTHING AND YOUR MECHANIC HAS CHECKED IT OUT.
COULD BE A RESULT OF THE CLIMATE WAS AT AND WEATHER CONDITIONS WHERE THE CAR HAS BEEN.

MIKE