Last month, a federal jury in Las Vegas convicted businessman Brent Kovar of running a scheme that took $24 million from at least 400 investors. Prosecutors said his company promised returns of 15 to 30 percent and claimed to have hundreds of millions of dollars in cryptocurrency reserves. It did not.

A month earlier, U.S. marshals in Nevada warned residents about scammers posing as deputy marshals and demanding cryptocurrency payments to clear fake warrants. In June, the Nevada attorney general warned about criminals directing victims to cryptocurrency kiosks.

The scams look different. The lesson is the same: Once the money is gone, getting it back can be extraordinarily difficult.

Nevadans reported more than $205 million in…