No matter the reason, the act of "resale of housing" (as most people wrongfully call it) is dishonest and wrong.
The game does not allow the selling of housing between players, and it's probably that way for a reason. If the ones buying houses become bored with it and don't want it anymore, their one and only option should be to simply relinquish it. If they aren't happy with losing the gil they spent, then maybe impulse buying of housing is what's the real problem. Think before buying; Am I really going to use it long enough to justify the price?
That's how the game is designed, whether you agree with it or not. If you were selling the house itself for the price you got it, it would be alright. Selling the act of relinquishing the house, even if it's for the price you paid it for, is still ripping someone off of gil they would normally not have to pay for the house, so it's wrong.
Sounds harsh? That's the housing system, though. No matter how flawed it is.
Just like it's annoying to you that you have to lose your gil if you don't want your house anymore, it's annoying for someone who wants a house but cannot find one due to it being limited.
There's downsides for both "sides", so there's no reason to pity anyone because they no longer want their house but they don't want to lose their investment. It's a selfish excuse that encourages a dishonest practice.
</endrant>