Please do not add a gil sink on top of a huge gil sink. The investment to a house is awful enough as it is, charge the guests to have to 'buy' the key off of the owner or something, make it a system where it is enforced. Do not punish the person who bought the house to pay more gil, then punish the person who bought the house with more gil if one of the friends they gave a key to goes bad.

I do not really like this system idea. It seems overcomplicated for something that could be implemented simply like a personal FC.