All house-flipping should be illegal. They are nothing more than get-rich-quick schemes for people who don't want to get real jobs. Impose a one-year minimum holding period on a house before you can sell it, plus a 110% tax on the difference between the purchase price and the selling price if less than a year. Example: you buy a house for $400k and sell it for $500k a month later. You pay a tax of $110k, no exceptions.