An armourer may specialize in a certain type of armour, or a particular quality level. For example, an armourer may make only maille, and another may build only munitions-grade pieces, and yet another craft only full harnesses for nobility.
The medieval armourer would likely have been able to live well off his craft. In today's world, all but the most skilled or dedicated armourers find the profession relegated to a part-time job or hobby.
The armourer must have several things: