Over the years, I’ve used it the classic blue Dawn dish soap to remove yellow sweat stains, make no-grate laundry detergent, and much more — it’s even in my trusty Ultimate Stain Remover Spray!

Officials believe that scalpers are buying the soap in bulk to make a killing through resale. The Blue Stick soap, billed as a “superstar stain remover,” is the top-selling item among a range ...