Pierino is good for the gold!

The pre-sliced ones tend to go bad sooner than whole, too.

Mushrooms go bad when they start shaking down school kids for their lunch money.

for future reference, mushrooms will keep better in a brown paper bad. At the very least, remove any plastic wrap and leave them open to the air in the fridge. They may shrivel a bit but they won't go slimey and fishy smelling.

When I first took a mushroom class, my instructor had some statistics about more people getting sick from mushrooms gone bad than from poisonous ones. He said that a lot of people either don't want to waste or are just so enamored of specific mushrooms that they push it further than they would for other foods.

Thank you so much! I had a feeling, but wanted to make sure I wasn't pointlessly wasting them.

I agree, your hunch is probably accurate. Once they begin to go moist, slimy is not far away. Time for the compost bin!

Mushrooms often seem a little moist to me. It's when they get slimy and/or smelling especially funky that I'll toss them.

If they are getting brown and mushy, they are probably bad. I'd toss them to be on the safe side if you have any concern.