That's not possible in me country. You can't return stuff once it's opened.
If KM is to be believed you can just buy, use and return stuff in Kanadia. Does that even go for CD's and DVD/Blu-rays?
Granted, I don't live in the land of mounties and mooses, but still, many places will allow you to return optical media if it is defective. Whether they believe you depends on how persuasive you are (cry a little and stomp your feet like a petulant little girl), whether they actually try to reproduce your "error" (nerds may), or how subtly you can damage the item yourself (devious...I like that). But this transaction is an exchange for another copy of the same item. You can't buy Slapshot, watch or copy it, and then try to exchange it for Mighty Ducks. You can only return it for a new copy of Slapshot, i.e. a replacement of the original item. Now that you have a new copy, you can return it anywhere. Hopefully you'll get cash but some places only give store credit because they're onto this kind of subtle scamming.
It sometimes helps to have a receipt from the original purchase if you're trying to stay honest, but you can always say it was a gift. Crummy places like Walmart don't care. You can take a half-eaten box of Cheetos back to Walmart saying it's stale, and they'll give you your money back. They don't care.