That's just my logic I don't deal in gift cards. I figure your best best to get the most would be via a trade (possibly for a gift card you can use). If you're selling it for cash -- you have to consider the buyers perspective:
1) Is it worth an hour of my time to meet this person to buy the gift card? Is gas involved how is that dipping into my savings?
2) Is it worth the risk -- I'm shelling out XXX dollars.... and it could get rejected if the person charge backs? Particularly for something you won't use instantly (such as a Starbucks gift card that you plan to use over weeks months, same goes for iTunes).
3) I'm giving up cash (can be spent on anything) for a gift card (can be only spent at one store) -- is the savings worth having to sell it in the event I don't end up using it all? Can I even sell it if I don't use it all?
I know I've been sitting on ~3000 in Apple Store Gift Cards -- which I figured I'd sell quickly but it's been months now. I keep getting people offering 1500, 2000, 2300.... for me as a seller I know I'll eventually use them if they don't sell and their not going to depreciate -- so I decline. I know at my asking they're saving a few hundred dollars so it at least addresses part 1 (is the hour or so worth the savings), and I've told them I can provide receipts dating back months to ensure they're not purchased on stolen cards which addresses part 2, but it seems over coming part 3 is still a big obstacle -- among other issues given their excessive value, or that audience is more likely to save more by buying used and would rather that than saving a little bit less and getting new. They're a tricky situation -- if the loss isn't worth it for you just hold on to them -- you may find some music, apps, that you'll use.