Looking to capitalize on South Florida’s booming waterfront mansion market, sellers of vacant waterfront lots in Miami and Miami Beach are listing their properties for prices that appear to bend reality. 

Sellers have been told that so many wealthy people are moving from California, Chicago and New York, big CEOs looking for properties like the billionaire Ken Griffin, who paid $106.9 million for a 4-acre Coconut Grove waterfront estate this summer.

But thanks to rising construction ...