The best way to tell if there has been any damage, from an accident, or a flood, is a very thorough inspection by a professional that knows what to look for.
As an example, we had our Jaguar automobile hit broadside by someone that ran a red light. State Farm totaled it, gave us a check, and sold the carcass to the dealer. The dealer repaired the extensive damage and sold the car within 30 days to an overseas buyer, with a clean CarFax. Apparently it takes awhile for the paperwork to catch up with a CarFax report.
The Chevrolet HHR that we are now using as a toad was purchased from Enterprise rental after it had received some minor hail damage. The out the door price was about 1/3 the MSRP for an 8,000 mile vehicle. The minor hail damage was enough to take the vehicle out of service as a rental, but since Enterprise Rental self-insures, there was no report to CarFax. I received a clean title. In other words, if you pull a CarFax report on my vehicle, it shows "no problems found" under hail damage. Basically what I am saying is do not trust a CarFax report to give you all of the information about possible problems with any vehicle.