find out what systems they put in place to mitigate future flooding. is there a sump pump (or two!), is that enough to deter any flooding and damage? as Sally says - get documentation, do not accept an email list or verbal.
you can check this site https://www.floodsmart.gov/floodsmart/pages/landing_pages/landing0000_1.jsp?WT.mc_id=FEMA_Google1&WT.srch=1 to see what the flood risk level is as designated by FEMA, and it'll tell you who to contact for flood ins rates, or give you an estimate on your annual flood ins premium.
if you make an offer on this property, make sure there is a provision in the contract language that lets you out if you don't like the ins rates or results of the documentation.