Some people honestly might.
I personally have found items on vendor that have been default priced or missing a 0. I could have kept them or sold them sometimes for over 100m profit... I choose to track down the owner and return the item. Now, I'm not trying to toot my own horn, the point I'm trying to make is that no one would have known, but -I- would. That goes against my personal set of morality. For someone else, it might be different. We don't know the minds of others or what they would or would not do. If a player feels very strongly against dupes, they might trash them. Others won't. You are entitled to voice your opinions, but please understand they are just that... opinions, not fact. On the other foot, tolerance is needed when interpreting others words. It might be their opinion that no one would do that. No one speaks for you, but you. Trust in that and don't let people's opinions get you riled up.
Now... let's get back to the topic.
For me personally if I find I have a dupe in my collection, it'll most likely stay in my collection. If I choose at some time to sell it, I'll disclose that fact to the buyer so they will make an informed offer. I may attempt to upgrade it to a non-duped version if it is one of my more favorite items. I'm far more interested in how the items fit into my home and my characters' rp than their rarity. ... besides if I didn't have my flask of human blood my vampire characters might run amok. I will be waiting to test my collection after the publish has been made and the bugs worked out. I want it to be free of bugs before I make any decisions especially since I'm so picky about which items I collect.