Woops! I bought the wrong item. (Too bad.)

[Silverbane]

Adding a return/refund system isn't going to suddenly cause FFXIV the player base to dry and profits to disappear.

You're being absurd; that's not the issue, it's a strawman of your own making.

This issue is: is there a decent ROI on the developer resources spent?
That is, is the subscriber base and/or revenue likely to increase as a result of adding this feature? And if so, is that increase likely to be larger than if the resources had been used to implement something else?

I seriously doubt this is the case: the presence or absence of this feature seems unlikely to affect many people's decision to subscribe or to continue their subscription, or to in any other way spend time or money on the game. Spending the same resources to add more high heeled shoes (such as for fem Vieras) likely has a higher ROI.