Fake bomb detectors
In the late 90's a $20 novelty golf-ball location device called a 'Gopher' was sold to golfers. it consisted of a dowsing-rod like appendage on a plastic gun stock. Clearly useless, they were then marketed as drug and bomb detecting kits and marked up in price hugely. Dismissed by US and the UK gov'ts, UK businessman James McCormick, bought a load and with friends Joan and Sam Tree, assembled some in a shed, added some new packaging and branding (now called the ADE-651) and sold them at a hugely inflated price to governments who were less able to test properly and were bribes could help the wheels move.
Iraq spent £53 million, and countries such as Mexico, Pakistan, Thailand and Egypt all bought them. McCormick and the Trees arranged for demonstrations - rigged to ensure they 'worked' - showing the detectors finding explosives, drugs, people, animals; in fact lots of different substances, with the help of a credit-card like piece of plastic for the particular substance you wanted to detect slotted into the device. Bear in mind there were no electronic or power generating components in these things. The were simply a swivelling car ariel protruding from a plastic gun.
Amazingly they received the help and assistance of the Foreign and Commonwealth office, the MOD and various government agencies to help promote and sell their Great British export. Eventually, thanks to dedicated journalists, especially Meirion Jones, the scam was exposed and the Trees and James McCormick given long prison sentences for fraud. But not before countless bombs had passed checkpoints undetected to kill or maim.