Agreed. But there are things you can still do -- vet the reputation of the dealer thoroughly. Be skeptical of prices that are too good to be true. There are also some signs of flood damaged cars you can look for when checking the car out on the lot.

https://auto.howstuffworks.com/under-the-hood/salvage-used-junkyard-parts/10-ways-to-spot-flood-damaged-car.htm