A shop worker sold a knife to an underage customer so long as they promised they 'wouldn't kill anyone' with it.
The store, in Wolverhampton, west Midlands, flogged the reduce-priced blade to the teenager this week.
West Midlands Police witnessed the £5 knife being sold to a 17-year-old, with the price having being slashed by more than half.
In the UK, it is illegal to sell knives and bladed products to people aged under 18.
Wolves City Centre Police tweeted: "We’re cracking down on premises selling knives in the city.
"Yesterday we saw a knife sold to a 17-year-old for £5 reduced from £12.99 as long as he didn’t kill anyone!"
They uncovered the sale as part of Operation Sceptre, a week-long campaign nationwide to tackle knife crime.
Earlier this year it was announced that number of fatal stabbings in England and Wales is at its highest level since records began more than 76 years ago.
Concerning Office for National Statistics show 282 homicides were committed using a knife or sharp instrument in the year to March 2022.
It is a 19% rise compared with the previous year, and the highest annual total since 1946 records began.