Besides the money concern, CDs I don't like can't be kept in my living room. And I don't have enough storage space to keep CDs and books that disappointed for long. Shipping from the Netherlands is expensive, so I hardly sell on eBay anymore. Only expensive items are worth the effort.
Storage space is mostly filled by old Blue Note CD masterings and duplicate Iain M. Banks Culture books. Otherwise it's straight to the garbage/recycling bin.