you will have to have a look yourself,maybe stone chips starting to rust,some manufacturers give a 10year body warranty but this may depend on where the motor has been serviced,wouldnt think testers would lift carpets etc to inspect inner sills,if it is not too bad a light sanding,q rust and a good primer and top coat may see you sorted,if you can also inject some waxoyl into sill areas too may help future problems
cdc, March 2011