Crystalizing is a problem with many liquids & powders BUT there are some products (like Radical and Retention+) which do not crystalize. Crystalization is caused by working in an environment which is too cold, OR the liquid is cold, OR the clients hands are cold, OR working in a draft etc. Or a combination of these things.
Keep your environment at a comfortable temperature and if your liquid is cold, it can be warmed by standing the bottle in warm water prior to the start of your working day if it has gone cold over night (remember to loosen the cap slightly to allow for expansion). There are also electric warming dishes available in the marketplace.(of course you would NEVER attempt to warm it ina microwave or anything like that would you?)
Warm clients hands by immersing up to the wrists in warm water for a minute or two prior to service.
Better still, choose a product that makes life easier for the technician.