Start by accepting that you can't kill it.

To kill it you need 2 things. 1, the removal of the 45 day demo timer and 2, the removal of the ability to relinquish plots. Its safe to say neither is going to happen.

The most extreme measure SE can do to discourage flipping is to not allow players to relinquish housing outside of the 45 day demolition timer which is a bad idea on its own. But even if SE did this house flipping would only slow down and increase the price because of the effort flippers have to go through for it. SE could also implement an function in the game for selling houses and put a limit on how much things will sell for which could put a limit on how much flippers can get away with. Both options taken together would remove a lot of incentive to flip houses but it won't stop it; both options also have their downsides for players too. The bottom line is, if flippers want to flip, they will.