Berlin is unique in that this city has some very tough housing laws. You're better off being a renter than an owner. Because of that flippers and investors have shied away.

I can't remember where I heard but the city controls the rental rates. Don't want to pay more for a property than you can recoup. And you don't want to leave it unoccupied less you come back to find it squatted; and they have rights as well.

Because it is so highly regulated its not a great investment.