Florida law requires that once a vehicle has been declared a total loss due to flood damage the certificate of title should be branded as such. It further requires the owner to disclose this damage to all potential buyers. But that doesn't prevent dishonest actions by dealers or individuals who import damaged cars and deceptively obtain new titles. The Florida Division of Motor Vehicles will do a search of a vehicle's history for a small fee, but there is no guarantee the owner has been honest about past damage. Look for silt in places it normally would not be such as inside door panels, under the spare tire and under the dash.
Silt is so fine it is impossible to get rid of all of it.
Look for any indication of a water line on the outside of the opaque plastic container that holds windshield washer fluid. Smell interior and trunk for damp or musty odors. New carpet or upholstery in an older vehicle may indicate flood damage. Usually all the fluids are not replaced at the same time. Look for rust on areas inside the car where it usually does not occur.