Selecting fresh mushrooms is not as easy as one might think. Some varieties exhibit different aspects of freshness than others. The feel, texture, smell and moisture of a mushroom, can provide a lot of information about how long ago it was harvested and what it’s storage life might be.
Personally, once I have found the mushroom I want to cook with, I will prepare and eat it within 24-hours. That is not to say that you have to treat all mushrooms this way, but I prefer the ones that look fresh, have a nice colour, are crisp and spongy, rather than those which are a bit soft, floppy or showing signs of discolouration.