A spoofer might stack a huge bid to make a stock look supported, buy on the ask once others follow, then cancel the bid. The Dodd-Frank Act made it a crime, and traders have received prison sentences for spoofing futures.
It is why large orders on level-2 that appear and vanish should not be trusted as real interest.
Example: 50,000 shares appear on the bid at $20.00 for three seconds, price ticks up as buyers react, and the order disappears without a single fill.
Related: market-manipulation, level-2, order-book, cftc