Since the OP did not write about his interactions with these sellers it is hard to know if he did or did not inform them. But I don't believe the OP was obligated in any way to tell everyone about Apple's warranty terms... so I don't think not telling them was a "dick move". I can also think of plenty of reasons why a person might know all those facts and still choose to sell the broken, still-in-warranty iPod. One of them being that you don't get a new iPod... you get a refurbished iPod and some people just don't want someone else's used stuff. Other people may have already upgraded to a new/different model and no longer need the broken one replaced.
"Other people may have already upgraded to a new/different model and no longer need the broken one replaced."
That was usually the case. People often felt they were due for an upgrade anyway and wanted to simply part ways rather than dealing with the warranty process.
I would gladly sell something under warranty rather than go through the pain of having to deal with a corporate. It is not a cost free transaction to complete a warranty claim, as our own time should be valued, and not all of us are that organised.
I did something similar with a MacBook Air after I broke its screen. I purchased a new MBA immediately, and eventually sold the old MBA to the repairer.
Efficient market hypothesis virtually demands this and instructs us that economies should be run by the free market because by acting on the information via the market we disseminate information about the supply/demand of goods and their alternative uses. By buying iPods under warranty he puts upwards pressure on price, disseminating information that an iPod under warranty is more valuable.
Sorry OP, just replying here so one of your commenters sees it:
schraeds, you've been hellbanned for the last 30 days, just FYI. I see you trying to post twice, but every comment you've made for the last 30 days has been auto-dead.
I honestly cannot figure out why, unless you deleted an atrocious violation of the rules or spam. Your last comment that wasn't auto-dead was about the "hippy generation", so maybe someone took offense with that?