It all depends on the return policy that the suppliers have with the stores. I used to work at Canadian Tire, and some suppliers will make you send the defective product back to them to receive credit, or tell you where to send it for repair, while others will just simply tell you to destroy the product and they will compensate you for your loss. If they tell you to destroy the product, you have to, you cannot sell it for a discounted price because of the fact that they are reimbursing you, and you cannot make that extra money. This is all up to the store if they want to make the claim in the first place. They can decide to not make a claim with the supplier at all, and just sell the product for a discounted price.
And back to the original question, no, I would not want to go dumpster diving. I do however, always wonder when I see a tv or something similar sitting next to the trash, if it actually works or not. I do always assume that it doesn't, but even if the item did work, they are normally quite old and shitty anyways.