Source? This sounds very urban legend. Most stores won't sell it as 'damaged stock' but they also reject many other products based entirely on external appearance regardless of whether they are fit for purpose or not.
That's more about the attractiveness of the product than safety. Those dented cans are sold somewhere else. Here's such a place near where I grew up: http://www.npsstore.com/about
I don't know if they still do it now, but years ago I noticed that the major super markets will actually sell any canned item that has a dent at a reduced price.
