** the heat and humidity inside a microwave...paints a homeowner would apply don't generally stand up to this sort of thing well... **
We use the same spray paint in business and it is what most of the microwave oven manufacturers recommend to be used in such cases. But I agree, if the surface is not prepared properly, I wouldn't expect it to last long either.
** why not just buy a new microwave??? **
1. Well the paint is $15 and a new microwave (one of the smaller ones) at least $50. That makes painting $35 cheaper.
2. People hate having to learn to program a new electronic devices and often prefer to keep what they already know.
3. Don't contribute to our land fills too quickly. One of the 3 R's in recycling is "Reuse".