Hi Teepee - didn't meant to sound so negative about rental yields - reading your post and re-reading mine I agree I could have explained better.
I don't meant to say or infer that buying tenanted properties in Berlin for the steady rental yield is an unsafe or unwise decision. However, I do feel that there is a better option which gives the buyers more freedom as well as potentially higher yields. The problem is the lack of units in which this latter option can be effectively run. (Sorry for the cryptic message but it's the USP which sets the company I work for out from the crowd so I can't give the game away without breaking my non-disclosure agreement. As far as I know we are the only ones doing it at the moment)
The "challenge" with tenanted properties is when agencies are selling properties with unrealistic yields either because they are going by what the developer told them without questioning it (ignorance) or because they are misleading their clients on purpose. While researching the market I came across many agencies who were offering tenanted properties promising monthly rentals at the top end of what is allowed by the Berliner Mietspiegel and the companies offering them were also saying that the rent could be increased 6% per year. If the monthly rentals are severely lower than what is allowed by the Mietspiegel, yes they can be raised by a maximum of 6% per year but only until they reach the limit outlined by the Mietspiegel.
While I was doing my research although I found a lot of "rogue" agents, I did find a few which had a good grasp on the current market. I can only assume by your post that you are one of them. Totally agree with what you mention in your post. Maybe meet up for an Eisbein one of these days when I'm in Germany next (shudder).