The Battle of Hastings
There used to be an electronics store called ‘Hastings’ where I grew up that sold both new and used electronics. They had a deal that if you traded in 3 used games of a common type (e.g. all ps2 games) you could get a brand new game for free, no strings attached, just free, any game of that system.
So I would go into the store buy 3 incredibly cheap used games (bass pro hunting or whatever it was called for 5$, they had dozens) and then walk out, double back, and then trade those in for a $60 brand new game.
I did this constantly for a few months while being harrassed by the managers there until they stopped the promotion.
Story credit: Reddit / [deleted]