and like someone mentioned, contamination is the biggest problem. mushrooms begin with mycelium (network of hyphae). The mycelium colonizes substrate (in PF TEK it is the Brown rice flour and verm), and then when introduced to blue light and air begins to form primordia, primodria form the shrooms. The mycelium however is also part of common moulds - it is not a distinct biological feature of "mushrooms". What I am trying to say is, the environment for mycelial growth of magic mushrooms is also the environment for unwated contamination (like bread mould). Once contamination occurs you cannot really save it, especially if its not colonized. You CANNOT eat a contaminated mushroom, it is just plain stupid to do so.
you will need a pressure cooker/autoclave if you want to actually experiment and develop "sterile technique".
when you fruit the mycelium, contamination is not as big of a deal since the mycelium has already got a firm hold on the substrate. Lack of fresh air is usually the biggest problem, and really dirty environment around the mushroom. There are several TEKs on the net that alleviate this problem.