Back in WoW when they implemented the trade-back system, we had people who would buy something, go to a raid or dungeon, and in the middle of the raid say, "hey guys wait for me just 5 min, I gotta go trade my gear".

So he goes back to the NPC, sell back his gear and rebuy them again to extend the trade-back time limit, and ask a warlock to pull him back to the raid entrance.

With FFXIV where Darklight sets don't have slots nor is there an enchanting system, it is even more tempting to do this just so one doesn't "buy something and immediately get a drop to replace it".

Hence bonded items should never be traded back for its full value.

Unbonded items, definitely. If you haven't used it ever, it's reasonable to accept that you bought it by mistake. It happens. So a tradeback for unbonded gear is great, just like how we could buy back stuff we sold accidentally to a vendor.

I don't feel uncomfortable with throwing away gear after it has served its purpose. There's nothing wrong with that.

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On a related note, when they (WoW) also implemented trading of loot drops for a certain amount of time after getting the drop, it brought out the worst in people again:
  • People would NEED even if they had it, just so they can advertise to sell it immediately.
  • People would NEED for their friends, so if you're the only PUG you virtually are rolling against more people than you should be.
  • People became careless because they know they can make a mistake.