It's a free market. People can list things for what they want.

I'm not certain how you consider it destroying the market unless it forces the costs of the item below minimum gil amount it costs to make the item. Since a lot of housing items can be made from 100% player gathered materials, any price set for those items is profit.

The good news is there are tens of thousands of different items to make in the game. You can switch to making different items until the price rebounds to what you feel is acceptable,

Also, the game works the same way in Japan that it works here. If prices there are only 10k, maybe the problem is really that the sellers here are greedy and jacking up prices well above what they should be?