GRAND RAPIDS, Mich. -- In the market for a good used car? Watch out for vehicles that sat submerged for days in the flooded streets of New Orleans, Biloxi or other Gulf Coast cities ravaged by Hurricane Katrina. Insurance companies usually purchase such vehicles from policyholders, declare them "totaled" and then sell them at auction to be resold for parts, many of which will still be suitable for use in other cars and trucks. But some unscrupulous dealers and wholesalers buy flood-damaged cars at scrap prices, clean them up, retitle them and resell them. The vehicles may look good, but...