In purchases where there is a lender involved, the lender has a resource to accomplish this task. The fee is charged to the buyer in the 800 series items on the HUD-1 Settlement Statement. The lender is, of course, protecting their loan asset by verification of the risk of damage or loss by flooding. If the property is at risk, it doesn't necessarily preclude a loan, but flood insurance could be required.
You can access FEMA flood maps online, and there are several providers of online flood certifications in the links at the end of this article.

