Is it safe to invest in a property to flip it in the economy?

Lets face it the economy has continued to drop. Back when flipping was hot the market was increasing every year so people were desperate to get there hand on properties. Well, my boyfriend wants to buy a duplex that was never finished in construction because the builders ran out of money. He wants to finish the construction and then re- sell them. If they dont sell he will have to rent them. Is he able to make money in this investment. Im worried he is going to dig himself in a hole if he makes an irrational decision.