This System needs to be changed. In the meanwhile they could simply avoid the House Flipping by placing a delay between the plot relinquish and the chance to buy the plot. For example there could be a day or 2 of delay with some kind of "House Finder" Feature to see which houses are gonna be avaiable and when. This way nobody would pay someone to sell a plot which they can't possibly get 100%.

However, House flipping isn't the only problem, there is high demand, and SE can't possibly provide further Wards to cover all the houses demands. Honestly I have absolutely no clue how these wards works, so I wouldn't be able to sort a good solution for this.