Here's why:

* High electrical conductivity: Metals are excellent conductors of electricity due to their free-moving electrons.

* Malleability: Metals can be hammered or pressed into different shapes without breaking, a property known as malleability.

* Luster: Metals have a shiny appearance, which is referred to as luster.

These properties are characteristic of metals, and while other substances might exhibit one or two of these traits, the combination of all three strongly points to a metallic substance.