You can test their fruit. Many of the so-called miracle workers end up being exposed in other areas, such as sexual immorality or financial crimes. If someone is being dishonest and deceptive in other areas, it's a pretty safe bet they're being deceptive about their ability to perform miracles.
Hence, if the claim of the physical supernatural manifestation is true then the message of who produced the manifestation must also me true. This seems to be the pattern in the Bible.
But today there is no manifestations to prove or disprove because we are simply being presented claims.
This is the point, unlike modern day "prophets" the Bible did not simply use claims of physical supernatural events but purposeful and public manifestations.