"How do you 'hide' the damage these cars have? ;-)"
Easy, pop a kick panel and inspect any ground cables, and exposed metal above the floor level. These cars start rusting within days of exposure, and you can usually see a waterline once the carpet and/or kick panels have been exposed. I've had the not-so-pleasure of informing numerous people that their cars were submersed at some point in their history, and not a single person has responded with anything similar to "oh yea, I already know that".