Its a simple math problem. I buy a home that will be built in 6 months for 350k. If the home values go down drastically in price to make the deal unprofitable, I bail and lose my 2k deposit.

Current comparable prices for the same type of home in the same area are going for 400K-435k.

The builder pays my closing costs if I use their lender. I use an 80/20 loan. I have paid nothing out of pocket. I put the home up for sale and take the 3k per month hit paying off the mortgage until I sell. My wife is an agent so I don't have to pay a listing agent, only the buyers agent. That takes out about 9k out of the deal. Assuming I have to hold onto the home for 4 months before it sells, this is what I stand to gain.

410k Sales Price - 350 PP - 9k commission - 0 closing costs - 4 *(3k) monthly payment = 39K profit

It still works if you know what you are doing and live in the right area.