I was told that there is synthetic Malachite being sold under the label of real. Is this true? Also they said you can test the malachite with nail polish remover or hot water. She said that the color and look of the stone is light/perfect and it's cheap to buy
Yes, I have seen synthetic Malachitein craft shops and inexpensive jewelry supply outlets. I have not used the nail polish or hot water tests, and would tend to avoid them because the acetone in nail polish remover could create a toxic chemical reaction with the unknown substance of an imitation and hot water can damage crystals, if it turns out to be real. Fake malachite, in my experience, is lighter weight than the real thing of the same size; it is softer and less shiny when polished; and the patterns are too regular--usually stripes. And the price is a good indicator. If it seems like a price that's too good to be true, it is!
Another way to tell the difference is to familiarize yourself with the energetic feel (vibration) of Malachite. If you tend to be able to sense the energy of crystals, once you have worked with some actual malachite from trustworthy sources, you will notice that the fake stuff feels "lifeless" or "just wrong" in your hands, and even in pictures, if you are that energy sensitive.