Crystals, like Quartz, have a very interesting molecular structure. This spiral formation is actually quite similar to your own bone structure, with overlapping layers that create a molecular spiral. Quartz is also piezoelectric, and can act as an energy filter like those used in electronics. Acting as a filter appears to be the main component of most of the crystals or stones that people are attracted to. So, in a polluted environment full of random types of energy flying around, a crystal will usually filter out everything but a narrow band of energy, but on a very small scale. To use them, you then need to sense that small energy left after filtering, and mimic it in your own sphere. So they can set the stage, or the tempo, and act like a metronome to base your energy on. Whether that energy is helpful depends on your own sphere of energy, and which parts of your energy are active and engaged with the surface of your sphere. Many types of stones or crystals can be used to help focus your own energy, by filtering out all the excess and only allowing certain energy formats to flow through. Even the color is a reflection of photons (light) being absorbed or bouncing off the surface. Photons are energy that can be absorbed, like plants using sunlight for photosynthesis.
Colors have their own place in magical practices, to include phantom colors used in practices like you have in Ophiel's "Art and Practice" series.
In one experiment, when people imagined a white light with their eyes close in a dark room, the photons they produced from their own skulls increased when measured in the lab, but only radiating from the right side of the head. So photon energy and visualization are connected in the real world of measuring and science. Most stones and crystals are neutral unless someone can connect them to an energy source, and thus are not automatically imbued with some energy. Sometimes belief is enough to supply an energy, but in most cases, creating an energetic crystal with a purpose is a special skill. Not everyone will have that skill just because they desire it. Some entities will also be attracted to certain things, like containers as housing, and may prefer certain stones or crystals for whatever reason they may have. Some will likely be driven away.
So, I would consider your position selling these items as similar to someone that sells herbs that can be used to help or heal. They have to be used properly, or combined properly, by the consumer. The person purchasing them is then responsible for proper preparation and use.