IIRC there are laws about it on the books from the Katrina days. Depends on the state, but we get a lot of used cars up here, and didn't see any from all that.
Flood cars have on major problem. The mechanicals will survive the dunking, 4WD guys mud their's and are constantly draining transmissions and differentials, pouring in new lube, etc. That survives well enough. The electricals do not.
Pass the word out that a flood car will have a 100% failure of the wiring harness over a period of months. First the injection starts acting up - those 0-5VDC circuits are easily affected. Then things like turn signals and brake lights quit working, door solenoids stop popping locks, and then the thing just won't even start and run. Every trip to the mechanic will get closer and closer together, more problems every time.
What happens is that the wire harness wicks up water under the insulation - any one end under water for an hour will pull water into it, and that water continues to spread by capillary action even if the flood waters drop later that day.
It's exactly why we sell off cars after ten years, too many things quit working. Planned obsolescence. Flooding one just accelerates the process, it only takes a few months after that.
I don't care what the price is, there's no such thing as a bargain flood car. Its a dead car rolling.