As with most unitary constructed cars the sills are vital to the strength of the structure, checking is difficult because of the cosmetic outer panel, check from inside the car by tapping the inner sill and lifting the carpet to assess the condition of the floor to sill join.
		From underneath inspect as much as possible of the sill, if the outer panel has been welded on be very wary as this is often a sign that any repairs have been bodged.