Slimy or sticky texture
Strong sour, fishy, or ammonia-like smell
Dark, wet, or moldy spots
Wrinkled, shriveled, or dried-out appearance
Mushrooms that are soft, mushy, or collapsing
Visible mold or fuzz
Discoloration beyond normal browning
Packaging that is swollen or leaking
Mushrooms past the expiration or use-by date
Any off smell, taste, or appearance after cooking