I’m split about whether or not that’s ‘immoral’, really… If the seller isn’t being massively exploited and the seller can be bothered listing separately, it’s not that bad.
I mean, that musical equipment I bought yesterday cost £40 for a tonne of things, yet the guy seemed to have an idea of what he’s talking about, so I didn’t question the price!

And I have already sold one of the items for £45, keeping the one I really wanted and still having another couple that will probably sell later. So, I effectively got paid £5 to get a piece of equipment that I wanted! Is this type of re-selling really bad? As I said, not always, I don’t think, as long as the seller is not being exploited maliciously. I don’t need or want the other bits that came as part of the deal, so why not sell them, for as much as I can get?
We have to assume that people are happy to take the price they have listed and that the goods can be used in whichever way afterwards (barring blasphemous usage or destruction

); we assume that the seller, obviously having the internet, had the opportunity to check prices and suchlike if they wanted to.
Sometimes, I will advise a seller that a price is far too low. However, yes, I hold my hands up and admit that the likelihood of this is significantly lower if I’m wanting to buy it myself…