How long after purchase will raw mushrooms remain good to eat?

There is no clear consensus. The conservative answer is that mushrooms should be eaten within two days of purchase. However, some experts maintain mushrooms will keep for up to a week after purchase, particularly if stored in cool, dry, and dark places. Pre-slicing mushrooms can shorten their shelf life. Once sliced, mushrooms quickly oxidate.  Some mushroom packagers recommend keeping raw mushrooms in a paper bag to keep them in good condition longer.
 
Because recommendations vary, inspect mushrooms carefully for signs of spoilage.
 
Source(s):
GourmetSleuth.com "Food Storage Guidelines"
Startcooking.com "How To: Mushrooms"
Wikianswers.com "How long do mushrooms stay fresh in the refrigerator?"
Health Canada "Safe Handling of Mushrooms"