Some wild mushrooms can be very toxic; therefore, mushrooms must always be purchased from a reliable and trustworthy commercial source.

Mushrooms can indeed be very toxic, with some wild varieties having the potential to cause serious illness or even death if consumed. The safest approach is to obtain mushrooms from reliable and trustworthy commercial sources, such as grocery stores or reputable farmers' markets, where they are properly identified and regulated for safety. This ensures that the mushrooms are safe for consumption and have not been misidentified, as many wild mushrooms can closely resemble edible varieties but may contain harmful toxins.

The other options imply that there could be exceptions to safety or that certain types of mushrooms are inherently safe, which can be misleading. For instance, while cultivated mushrooms are generally safe, the statement about all mushrooms being safe if cooked is also incorrect, as cooking does not eliminate the toxins present in some wild mushrooms. This reinforces the importance of sourcing mushrooms from reputable commercial operations to avoid the risk of toxicity.