what is the best way to inspect for frame damage?

Is it usually pretty obvious if a car has had frame damage?

It depends on what kind of damage your looking for.

Put it in the air and look from as far below it as you can. Maybe put the car up as high as the lift will take it and lay on a creeper.

It's a unibody car, so "frame" damage usually results in a healthy crumple =P

Or welds in places they should not be.Patching,etc.I do believe there was a post in other cars some time wayyyyy back about such issues but think it was geared more towards buying a used car,and difference in a salvage title car or something.I may suggest chkg the old post or Mrgoodwrench he may have shared it,Idk going on memory.

sometimes paint will be missing from where the flexing of the metal occured from the impact. some things will not be visible and an alignment is the only way to detect damaged components. that is why an alignment is done after collision repair.

A body shop will take measurements from fixed points on the underside of the car and compare this measurement to specs, and also compare left and right side measurements.